Method and apparatus for efficient feedback in a wireless communication system supporting multiple antenna

ABSTRACT

A method for transmitting channel status information (CSI) via uplink in a wireless communication system includes transmitting a first precoding matrix indicator (PMI) and a second PMI at a subframe. A subsampled codebook for each of a precoding codebook for Rank-1 and a precoding codebook for Rank-2 is determined based on at least the first PMI or the second PMI. In case of the Rank-1 or the Rank-2, a number of elements for the first PMI is 8.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, andmore particularly to a method and apparatus for performing effectivefeedback in a wireless communication system supporting multipleantennas.

2. Discussion of the Related Art

Generally, Multiple-Input Multiple-Output (MIMO) technology willhereinafter be described in detail. In brief, MIMO is an abbreviationfor Multi-Input Multi-Output. MIMO technology uses multiple transmission(Tx) antennas and multiple reception (Rx) antennas to improve theefficiency of transmission/reception (Tx/Rx) data, whereas theconventional art generally uses a single transmission (Tx) antenna and asingle reception (Rx) antenna. In other words, MIMO technology allows atransmitting end and a receiving end to use multiple antennas so as toincrease capacity or improve performance. If necessary, the MIMOtechnology may also be called multi-antenna technology. In order tocorrectly perform multi-antenna transmission, the MIMO system has toreceive feedback information regarding channels from a receiving enddesigned to receive multi-antenna channels.

Various feedback information fed back from the receiving end to thetransmitting end in the legacy MIMO wireless communication system may bedefined, for example, a rank indicator (RI), a precoding matrix index(PMI), channel quality information (CQI), etc. Such feedback informationmay be configured as information appropriate for the legacy MIMOtransmission.

There is a need for the new system including the extended antennaconfiguration as compared to the legacy MIMO wireless communicationsystem to be developed and introduced to the market. For example,although the legacy system can support a maximum of 4 transmissionantennas, the new system having the extended antenna configurationsupports MIMO transmission based on 8 transmission antennas, resultingin increased system capacity.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method and apparatusfor performing efficient feedback in a wireless communication systemsupporting multiple antennas that substantially obviate one or moreproblems due to limitations and disadvantages of the related art. Thenew system supporting the extended antenna configuration is designed toperform more complicated MIMO transmission than the legacy MIMOtransmission operation, such that it is impossible to correctly supportthe MIMO operation for the new system only using feedback informationdefined for the legacy MIMO transmission operation.

An object of the present invention is to provide a method and apparatusfor configuring and transmitting feedback information used for correctlyand efficiently support the MIMO operation based on the extended antennaconfiguration.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for transmitting channel status information (CSI) of downlinktransmission via uplink in a wireless communication system includestransmitting a rank indicator (RI) at a first subframe; and transmittinga first precoding matrix indicator (PMI), a second PMI, and a wideband(WB) channel quality indicator (CQI) at a second subframe, wherein auser equipment (UE) preferred precoding matrix is indicated by acombination of the first PMI and the second PMI, and a subsampledcodebook for each precoding codebook of ranks from Rank-1 to Rank-4 isapplied to the first PMI and the second PMI, and a sum of the first PMIand the second PMI for each of Rank-1 to Rank-4 is comprised of 4 bits.

In another aspect of the present invention, a method for receivingchannel status information (CSI) of downlink transmission via uplink ina wireless communication system includes receiving a rank indicator (RI)at a first subframe; and receiving a first precoding matrix indicator(PMI), a second PMI, and a wideband (WB) channel quality indicator (CQI)at a second subframe, wherein a user equipment (UE) preferred precodingmatrix is indicated by a combination of the first PMI and the secondPMI, and a subsampled codebook for each precoding codebook of ranks fromRank-1 to Rank-4 is applied to the first PMI and the second PMI, and asum of the first PMI and the second PMI for each of Rank-1 to Rank-4 iscomprised of 4 bits.

In another aspect of the present invention, a user equipment (UE) fortransmitting channel status information (CSI) of downlink transmissionvia uplink in a wireless communication system includes a receptionmodule for receiving a downlink signal from a base station (BS); atransmission module for transmitting an uplink signal to the basestation (BS); and a processor for controlling the user equipment (UE)including the reception module and the transmission module, wherein theprocessor, through the transmission module, transmits a rank indicator(RI) at a first subframe, and transmits a first precoding matrixindicator (PMI), a second PMI, and a wideband (WB) channel qualityindicator (CQI) at a second subframe, a UE preferred precoding matrix isindicated by a combination of the first PMI and the second PMI, and asubsampled codebook for each precoding codebook of ranks from Rank-1 toRank-4 is applied to the first PMI and the second PMI, and a sum of thefirst PMI and the second PMI for each of Rank-1 to Rank-4 is comprisedof 4 bits.

In another aspect of the present invention, a base station (BS) forreceiving channel status information (CSI) of downlink transmission viauplink in a wireless communication system includes a reception modulefor receiving an uplink signal from a user equipment (UE); atransmission module for transmitting a downlink signal to the userequipment (UE); and a processor for controlling the base station (BS)including the reception module and the transmission module, wherein theprocessor, through the reception module, receives a rank indicator (RI)at a first subframe, and receives a first precoding matrix indicator(PMI), a second PMI, and a wideband (WB) channel quality indicator (CQI)at a second subframe, a UE preferred precoding matrix is indicated by acombination of the first PMI and the second PMI, and a subsampledcodebook for each precoding codebook of ranks from Rank-1 to Rank-4 isapplied to the first PMI and the second PMI, and a sum of the first PMIand the second PMI for each of Rank-1 to Rank-4 is comprised of 4 bits.

The following characteristics can be commonly applied to theabove-mentioned embodiments of the present invention.

In association with each of the Rank-1 and the Rank-2, the first PMI maybe comprised of 3 bits in the subsampled codebook, and the second PMImay be comprised of 1 bit.

The precoding codebook for the Rank-1 is represented by the followingtable:

TABLE i₂ i₁ 0 1 2 3 0-15 W_(2i) ₁ _(,0) ⁽¹⁾ W_(2i) ₁ _(,1) ⁽¹⁾ W_(2i) ₁_(,2) ⁽¹⁾ W_(2i) ₁ _(,3) ⁽¹⁾ i₂ i₁ 4 5 6 7 0-15 W_(2i) ₁ _(+1,0) ⁽¹⁾W_(2i) ₁ _(+1,1) ⁽¹⁾ W_(2i) ₁ _(+1,2) ⁽¹⁾ W_(2i) ₁ _(+1,3) ⁽¹⁾ i₂ i₁ 8 910 11 0-15 W_(2i) ₁ _(+2,0) ⁽¹⁾ W_(2i) ₁ _(+2,1) ⁽¹⁾ W_(2i) ₁ _(+2,2)⁽¹⁾ W_(2i) ₁ _(+2,3) ⁽¹⁾ i₂ i₁ 12 13 14 15 0-15 W_(2i) ₁ _(+3,0) ⁽¹⁾W_(2i) ₁ _(+3,1) ⁽¹⁾ W_(2i) ₁ _(+3,2) ⁽¹⁾ W_(2i) ₁ _(+3,3) ⁽¹⁾${{where}\mspace{14mu} W_{m,n}^{(1)}} = {\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m} \\{\phi_{n}v_{m}}\end{bmatrix}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), and

in case of the Rank-1, the first PMI is set to any one of 0, 2, 4, 6, 8,10, 12 and 14, and the second PMI is set to any one of 0 and 2.

The precoding codebook for the Rank-2 is represented by the followingtable:

TABLE i₂ i₁ 0 1 2 3 0-15 W_(2i) ₁ _(,2i) ₁ _(,0) ⁽²⁾ W_(2i) ₁ _(,2i) ₁_(,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,1)⁽²⁾ i₂ i₁ 4 5 6 7 0-15 W_(2i) ₁ _(+2,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+2,2i)₁ _(+2,1) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁_(+3,1) ⁽²⁾ i₂ i₁ 8 9 10 11 0-15 W_(2i) ₁ _(,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁_(,2i) ₁ _(+1,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁_(+2,1) ⁽²⁾ i₂ i₁ 12 13 14 15 0-15 W_(2i) ₁ _(,2i) ₁ _(+3,0) ⁽²⁾ W_(2i)₁ _(,2i) ₁ _(+3,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+1,2i)₁ _(+3,1) ⁽²⁾${{where}\mspace{14mu} W_{m,m^{\prime},n}^{(2)}} = {\frac{1}{4}\begin{bmatrix}v_{m} & v_{m^{\prime}} \\{\phi_{n}v_{m}} & {{- \phi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), and

in case of the Rank-2, the first PMI is set to any one of 0, 2, 4, 6, 8,10, 12 and 14, and the second PMI is set to any one of 0 and 1.

In association with each of the Rank-3 and the Rank-4, the first PMI iscomprised of 1 bit in the subsampled codebook, and the second PMI iscomprised of 3 bits.

The precoding codebook for the Rank-3 is represented by the followingtable:

TABLE i₂ i₁ 0 1 2 3 0-3 W_(8i) ₁ _(,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ W_(8i) ₁_(+8,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(,8i) ₁ _(+8,8i) ₁₊₈ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+8,8i) ₁ _(,8i) ₁ ⁽³⁾ i₂ i₁ 4 5 6 7 0-3W_(8i) ₁ _(+2,8i) ₁ _(+2,4i) ₁ ₊₁₀ ⁽³⁾ W_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁₊₁₀ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+2,8i) ₁ _(+10,8i) ₁ ₊₁₀ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁ ₊₂ ⁽³⁾ i₂ i₁ 8 9 10 11 0-3W_(8i) ₁ _(+4,8i) ₁ _(+4,8i) ₁ ₊₁₂ ⁽³⁾ W_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁₊₁₂ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+4,8i) ₁ _(+12,8i) ₁ ₊₁₂ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁ ₊₄ ⁽³⁾ i₂ i₁ 12 13 14 15 0-3W_(8i) ₁ _(+6,8i) ₁ _(+6,8i) ₁ ₊₁₄ ⁽³⁾ W_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁₊₁₄ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+6,8i) ₁ _(+14,8i) ₁ ₊₁₄ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁ ₊₆ ⁽³⁾${{{where}\mspace{14mu} W_{m,m^{\prime},m^{''}}^{(3)}} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & {- v_{m^{\prime}}} & {- v_{m^{''}}}\end{bmatrix}}},{{\overset{\sim}{W}}_{m,m^{\prime},m^{''}}^{(3)} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & v_{m^{\prime}} & {- v_{m^{''}}}\end{bmatrix}}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), and

in case of the Rank-3, the first PMI is set to any one of 0 and 2, andthe second PMI is set to any one of 0, 1, 2, 3, 8, 9, 10 and 11.

The precoding codebook for the Rank-4 is represented by the followingtable:

TABLE i₂ i₁ 0 1 2 3 0-3 W_(8i) ₁ _(,8i) ₁ _(+8,0) ⁽⁴⁾ W_(8i) ₁ _(,8i) ₁_(+8,1) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁ _(+10,0) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁_(+10,1) ⁽⁴⁾ i₂ i₁ 4 5 6 7 0-3 W_(8i) ₁ _(+4,8i) ₁ _(+12,0) ⁽⁴⁾ W_(8i) ₁_(+4,8i) ₁ _(+12,1) ⁽⁴⁾ W_(8i) ₁ _(+6,8i) ₁ _(+14,0) ⁽⁴⁾ W_(8i) ₁_(+6,8i) ₁ _(+14,1) ⁽⁴⁾${{where}\mspace{14mu} W_{m,m^{\prime},n}^{(4)}} = {\frac{1}{\sqrt{32}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m} & v_{m^{\prime}} \\{\phi_{n}v_{m}} & {\phi_{n}v_{m^{\prime}}} & {{- \phi_{n}}v_{m}} & {{- \phi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T),and

in case of the Rank-4, the first PMI is set to any one of 0 and 2, andthe second PMI is set to any one of 0, 1, 2, 3, 4, 5, 6 and 7.

The RI is transmitted over a physical uplink control channel (PUCCH) ofthe first subframe, and the first PMI, the second PMI, and the CQI aretransmitted over a PUCCH of the second subframe.

The RI, the first PMI, the second PMI, and the CQI are contained inchannel status information (CSI) of downlink 8 transmission (Tx)antennas.

The RI is transmitted according to a first report cycle, and the firstPMI, the second PMI, and the CQI are transmitted according to a secondreport cycle.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

As apparent from the above description, exemplary embodiments of thepresent invention have the following effects. The embodiments of thepresent invention provide a method and apparatus for configuring andtransmitting feedback information used for correctly and efficientlysupport the MIMO operation based on the extended antenna configuration.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved with the present invention are not limitedto what has been particularly described hereinabove and other advantagesof the present invention will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system;

FIG. 2 exemplarily shows a resource grid of a downlink (DL) slot;

FIG. 3 is a downlink (DL) subframe structure;

FIG. 4 is an uplink (UL) subframe structure;

FIG. 5 shows a physical layer (L1) and a MAC layer (L2) of amulti-carrier supported system;

FIG. 6 is a conceptual diagram illustrating downlink (DL) and uplink(UL) component carriers (CCs);

FIG. 7 shows an exemplary linkage of DL/UL CCs;

FIG. 8 is a conceptual diagram illustrating an SC-FDMA transmissionscheme and an OFDMA transmission scheme;

FIG. 9 is a conceptual diagram illustrating maximum transmission powerfor single antenna transmission and MIMO transmission;

FIG. 10 is a conceptual diagram illustrating a MIMO communicationsystem;

FIG. 11 is a conceptual diagram illustrating a general CDD structure foruse in a MIMO system;

FIG. 12 is a conceptual diagram illustrating codebook-based precoding;

FIG. 13 shows a resource mapping structure of PUCCH;

FIG. 14 shows a channel structure of a CQI information bit;

FIG. 15 is a conceptual diagram illustrating transmission of CQI andACK/NACK information;

FIG. 16 is a conceptual diagram illustrating feedback of channel statusinformation;

FIG. 17 shows an example of a CQI report mode;

FIG. 18 is a conceptual diagram illustrating a method for enabling auser equipment (UE) to periodically transmit channel information;

FIG. 19 is a conceptual diagram illustrating SB CQI transmission;

FIG. 20 is a conceptual diagram illustrating transmission of WB CQI andSB CQI;

FIG. 21 is a conceptual diagram illustrating transmission of WB CQI, SBCQI and RI;

FIG. 22 is a flowchart illustrating a method for transmitting channelstatus information; and

FIG. 23 is a block diagram illustrating an eNB apparatus and a userequipment (UE) apparatus according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toanother. Some components or characteristics of any embodiment may alsobe included in other embodiments, or may be replaced with those of theother embodiments as necessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a terminal.In this case, the base station is used as a terminal node of a networkvia which the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “Base Station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with a Relay Node (RN) ora Relay Station (RS). The term “terminal” may also be replaced with aUser Equipment (UE), a Mobile Station (MS), a Mobile Subscriber Station(MSS) or a Subscriber Station (SS) as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for the convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system,and a 3GPP2 system. In particular, the steps or parts, which are notdescribed to clearly reveal the technical idea of the present invention,in the embodiments of the present invention may be supported by theabove documents. All terminology used herein may be supported by atleast one of the above-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, CDMA (CodeDivision Multiple Access), FDMA (Frequency Division Multiple Access),TDMA (Time Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier Frequency DivisionMultiple Access), and the like. The CDMA may be embodied with wireless(or radio) technology such as UTRA (Universal Terrestrial Radio Access)or CDMA2000. The TDMA may be embodied with wireless (or radio)technology such as GSM (Global System for Mobile communications)/GPRS(General Packet Radio Service)/EDGE (Enhanced Data Rates for GSMEvolution). The OFDMA may be embodied with wireless (or radio)technology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and E-UTRA(Evolved UTRA). The UTRA is a part of the UMTS (Universal MobileTelecommunications System). The 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of the E-UMTS (EvolvedUMTS), which uses E-UTRA. The 3GPP LTE employs the OFDMA in downlink andemploys the SC-FDMA in uplink. The LTE-Advanced (LTE-A) is an evolvedversion of the 3GPP LTE. WiMAX can be explained by an IEEE 802.16e(WirelessMAN-OFDMA Reference System) and an advanced IEEE 802.16m(WirelessMAN-OFDMA Advanced System). For clarity, the followingdescription focuses on the 3GPP LTE and 3GPP LTE-A system. However,technical features of the present invention are not limited thereto.

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system. Adownlink (DL) radio frame structure will hereinafter be described withreference to FIG. 1. In a cellular Orthogonal Frequency DivisionMultiplexing (OFDM) radio packet communication system, uplink/downlinkdata packet transmission is performed in subframe units. One subframe isdefined as a predetermined time interval including a plurality of OFDMsymbols. The 3GPP LTE standard supports a type 1 radio frame structureapplicable to Frequency Division Duplex (FDD) and a type 2 radio framestructure applicable to Time Division Duplex (TDD).

FIG. 1( a) is a diagram showing the structure of the type 1 radio frame.A downlink radio frame includes 10 subframes, and one subframe includestwo slots in a time region. A time required for transmitting onesubframe is defined in a Transmission Time Interval (TTI). For example,one subframe may have a length of 1 ms and one slot may have a length of0.5 ms. One slot may include a plurality of OFDM symbols in a timeregion and include a plurality of Resource Blocks (RBs) in a frequencyregion. Since the 3GPP LTE system uses OFDMA in downlink, the OFDMsymbol indicates one symbol duration. The OFDM symbol may be called anSC-FDMA symbol or a symbol duration. RB is a resource allocation unitand includes a plurality of contiguous carriers in one slot.

The number of OFDM symbols included in one slot may be changed accordingto the configuration of a Cyclic Prefix (CP). The CP includes anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be seven. If the OFDM symbols are configured by the extendedCP, the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is less than that of the case of the normalCP. In case of the extended CP, for example, the number of OFDM symbolsincluded in one slot may be six. If the channel state is unstable, forexample, if a User Equipment (UE) moves at a high speed, the extended CPmay be used in order to further reduce interference between symbols.

In case of using the normal CP, since one slot includes seven OFDMsymbols, one subframe includes 14 OFDM symbols. At this time, the firsttwo or three OFDM symbols of each subframe may be allocated to aPhysical Downlink Control Channel (PDCCH) and the remaining OFDM symbolsmay be allocated to a Physical Downlink Shared Channel (PDSCH).

The structure of a type 2 radio frame is shown in FIG. 1( b). The type 2radio frame includes two half-frames, each of which is made up of fivesubframes, a downlink pilot time slot (DwPTS), a guard period (GP), andan uplink pilot time slot (UpPTS), in which one subframe consists of twoslots. That is, one subframe is composed of two slots irrespective ofthe radio frame type. DwPTS is used to perform initial cell search,synchronization, or channel estimation. UpPTS is used to perform channelestimation of a base station and uplink transmission synchronization ofa user equipment (UE). The guard interval (GP) is located between anuplink and a downlink so as to remove interference generated in theuplink due to multi-path delay of a downlink signal. That is, onesubframe is composed of two slots irrespective of the radio frame type.

The structure of the radio frame is only exemplary. Accordingly, thenumber of subframes included in the radio frame, the number of slotsincluded in the subframe or the number of symbols included in the slotmay be changed in various manners.

FIG. 2 is a diagram showing a resource grid in a downlink slot. Althoughone downlink slot includes seven OFDM symbols in a time domain and oneRB includes 12 subcarriers in a frequency domain in the figure, thescope or spirit of the present invention is not limited thereto. Forexample, in case of a normal Cyclic Prefix (CP), one slot includes 7OFDM symbols. However, in case of an extended CP, one slot may include 6OFDM symbols. Each element on the resource grid is referred to as aresource element. One RB includes 12×7 resource elements. The number NDLof RBs included in the downlink slot is determined based on downlinktransmission bandwidth. The structure of the uplink slot may be equal tothe structure of the downlink slot.

FIG. 3 is a diagram showing the structure of a downlink subframe. Amaximum of three OFDM symbols of a front portion of a first slot withinone subframe corresponds to a control region to which a control channelis allocated. The remaining OFDM symbols correspond to a data region towhich a Physical Downlink Shared Channel (PDSCH) is allocated. The basicunit of transmission becomes one subframe. Examples of the downlinkcontrol channels used in the 3GPP LTE system include, for example, aPhysical Control Format Indicator Channel (PCFICH), a Physical DownlinkControl Channel (PDCCH), a Physical Hybrid automatic repeat requestIndicator Channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe, and includes information about the number ofOFDM symbols used to transmit the control channel in the subframe.

The PHICH includes a HARQ ACK/NACK signal as a response to uplinktransmission. The control information transmitted through the PDCCH isreferred to as Downlink Control Information (DCI). The DCI includesuplink or downlink scheduling information or an uplink transmit powercontrol command for a certain UE group. The PDCCH may include resourceallocation and transmission format of a Downlink Shared Channel(DL-SCH), resource allocation information of an Uplink Shared Channel(UL-SCH), paging information of a Paging Channel (PCH), systeminformation on the DL-SCH, resource allocation of a higher layer controlmessage such as a Random Access Response (RAR) transmitted on the PDSCH,a set of transmit power control commands for individual UEs in a certainUE group, transmit power control information, activation of Voice overIP (VoIP), etc. A plurality of PDCCHs may be transmitted within thecontrol region. The UE may monitor the plurality of PDCCHs. The PDCCHsare transmitted on an aggregation of one or several contiguous controlchannel elements (CCEs). The CCE is a logical allocation unit used toprovide the PDCCHs at a coding rate based on the state of a radiochannel. The CCE corresponds to a plurality of resource element groups.The format of the PDCCH and the number of available bits are determinedbased on a correlation between the number of CCEs and the coding rateprovided by the CCEs. The base station determines a PDCCH formataccording to a DCI to be transmitted to the UE, and attaches a CyclicRedundancy Check (CRC) to control information. The CRC is masked with aRadio Network Temporary Identifier (RNTI) according to an owner or usageof the PDCCH. If the PDCCH is for a specific UE, a cell-RNTI (C-RNTI) ofthe UE may be masked to the CRC. Alternatively, if the PDCCH is for apaging message, a paging indicator identifier P-RNTI) may be masked tothe CRC. If the PDCCH is for system information (more specifically, asystem information block (SIB)), a system information identifier and asystem information RNTI (SI-RNTI) may be masked to the CRC. To indicatea random access response that is a response for transmission of a randomaccess preamble of the UE, a random access-RNTI (RA-RNTI) may be maskedto the CRC.

FIG. 4 is a diagram showing the structure of an uplink frame. The uplinksubframe may be divided into a control region and a data region in afrequency region. A Physical Uplink Control Channel (PUCCH) includinguplink control information is allocated to the control region. APhysical uplink Shared Channel (PUSCH) including user data is allocatedto the data region. In order to maintain single carrier characteristics,one UE does not simultaneously transmit the PUCCH and the PUSCH. ThePUCCH for one UE is allocated to an RB pair in a subframe. RBs belongingto the RB pair occupy different subcarriers with respect to two slots.Thus, the RB pair allocated to the PUCCH is “frequency-hopped” at a slotedge.

Carrier Aggregation

Although downlink and uplink bandwidths are different from each other, awireless communication system typically uses one carrier. For example, awireless communication system having one carrier for each of thedownlink and the uplink and symmetry between the downlink and uplinkbandwidths may be provided based on a single carrier.

The International Telecommunication Union (ITU) requests thatIMT-Advanced candidates support wider bandwidths, compared to legacywireless communication systems. However, allocation of a wide frequencybandwidth is difficult throughout most of the world. Accordingly, atechnology for efficiently using small segmented bands, known as carrieraggregation (bandwidth aggregation) or spectrum aggregation, has beendeveloped in order to aggregate a plurality of physical bands to alogical wider band.

Carrier aggregation was introduced to support increased throughput,prevent a cost increase caused by introduction of wideband RF devices,and ensure compatibility with legacy systems. Carrier aggregationenables data exchange between a UE and an eNB through a group ofcarriers each having a bandwidth unit defined in a legacy wirelesscommunication system (e.g. 3GPP LTE Release-8 or Release-9 in case of3GPP LTE-A). The carriers each having a bandwidth unit defined in thelegacy wireless communication system may be called Component Carriers(CCs). Carrier aggregation using one or more CCs may be applied to eachof the downlink and the uplink. Carrier aggregation may support a systembandwidth of up to 100 MHz by aggregating up to five CCs each having abandwidth of 5, 10 or 20 MHz.

A downlink CC and an uplink CC may be represented as a DL CC and a ULCC, respectively. A carrier or CC may be represented as a cell in termsof function in the 3GPP LTE system. Thus, a DL CC and a UL CC may bereferred to as a DL cell and a UL cell, respectively. Hereinbelow, theterms ‘carriers’, ‘component carriers’, ‘CCs’ or ‘cells’ will be used tosignify a plurality of carriers to which carrier aggregation is applied.

While the following description exemplarily uses an eNB (BS) or cell asa downlink transmission entity and exemplarily uses a UE as an uplinktransmission entity, the scope or spirit of the present invention is notlimited thereto. That is, even when a relay node (RN) may be used as adownlink transmission entity from an eNB to a UE and or be used as anuplink reception entity from a UE to an eNB, or even when the RN may beused an uplink transmission entity for a UE or be used as a downlinkreception entity from an eNB, it should be noted that the embodiments ofthe present invention can be applied without difficulty.

Downlink carrier aggregation may be described as an eNB supportingdownlink transmission to a UE in frequency resources (subcarriers orphysical resource blocks [PRBs]) of one or more carrier bands in timeresources (allocated in units of a subframe). Uplink carrier aggregationmay be described as a UE supporting uplink transmission to an eNB infrequency resources (subcarriers or PRBs) of one or more carrier bandsin time resources (allocated in units of a subframe).

FIG. 5 shows a physical layer (first layer, L1) and a MAC layer (secondlayer, L2) of a multi-carrier supported system. Referring to FIG. 5, aneNB or BS of the legacy wireless communication system supporting asingle carrier includes one physical layer (PHY) entity capable ofsupporting one carrier, and one medium access control (MAC) entity forcontrolling one PHY entity may be provided to the eNB. For example,baseband processing may be carried out in the PHY layer. For example,the L1/L2 scheduler operation including not only MAC PDU (Protocol DataUnit) creation of a transmitter but also MAC/RLC sub-layers may becarried out in the MAC layer. The MAC PDU packet block of the MAC layeris converted into a transport block through a logical transport layer,such that the resultant transport block is mapped to a physical layerinput information block. In FIG. 5, the MAC layer is represented as theentire L2 layer, and may conceptually cover MAC/RLC/PDCP sub-layers. Forconvenience of description and better understanding of the presentinvention, the above-mentioned application may be used interchangeablyin the MAC layer description of the present invention.

On the other hand, a multicarrier-supported system may provide aplurality of MAC-PHY entities. In more detail, as can be seen from FIG.5( a), the transmitter and receiver of the multicarrier-supported systemmay be configured in such a manner that one MAC-PHY entity is mapped toeach of n component carriers (n CCs). An independent PHY layer and anindependent MAC layer are assigned to each CC, such that a PDSCH foreach CC may be created in the range from the MAC PDU to the PHY layer.

Alternatively, the multicarrier-supported system may provide one commonMAC entity and a plurality of PHY entities. That is, as shown in FIG. 5(b), the multicarrier-supported system may include the transmitter andthe receiver in such a manner that n PHY entities respectivelycorrespond to n CCs and one common MAC entity controlling the n PHYentities may be present in each of the transmitter and the receiver. Inthis case, a MAC PDU from one MAC layer may be branched into a pluralityof transport blocks corresponding to a plurality of CCs through atransport layer. Alternatively, when generating a MAC PDU in the MAClayer or when generating an RLC PDU in the RLC layer, the MAC PDU or RLCPDU may be branched into individual CCs. As a result, a PDSCH for eachCC may be generated in the PHY layer.

PDCCH for transmitting L1/L2 control signaling control informationgenerated from a packet scheduler of the MAC layer may be mapped tophysical resources for each CC, and then transmitted. In this case,PDCCH that includes control information (DL assignment or UL grant) fortransmitting PDSCH or PUSCH to a specific UE may be separately encodedat every CC to which the corresponding PDSCH/PUSCH is transmitted. ThePDCCH may be called a separate coded PDCCH. On the other hand,PDSCH/PUSCH transmission control information of several CCs may beconfigured in one PDCCH such that the configured PDCCH may betransmitted. This PDCCH may be called a joint coded PDCCH.

To support carrier aggregation, connection between a BS (or eNB) and aUE (or RN) needs to be established and preparation of connection setupbetween the BS and the UE is needed in such a manner that a controlchannel (PDCCH or PUCCH) and/or a shared channel (PDSCH or PUSCH) can betransmitted. In order to perform the above-mentioned connection orconnection setup for a specific UE or RN, measurement and/or reportingfor each carrier are needed, and CCs serving as the measurement and/orreporting targets may be assigned. In other words, CC assignment meansthat CCs (indicating the number of CCs and indexes of CCs) used forDL/UL transmission are established in consideration of not onlycapability of a specific UE (or RN) from among UL/DL CCs constructed inthe BS but also the system environments.

In this case, when CC assignment is controlled in third layer (L3) RadioResource Management (RRM), UE-specific or RN-specific RRC signaling maybe used. Alternatively, cell-specific or cell cluster-specific RRCsignaling may be used. Provided that dynamic control such as a series ofCC activation/deactivation setting is needed for CC assignment, apredetermined PDCCH may be used as L1/L2 control signaling, or adedicated physical control channel for CC assignment control informationor an L2 MAC-message formatted PDSCH may be used. On the other hand, ifCC assignment is controlled by a packet scheduler, a predetermined PDCCHmay be used as L1/L2 control signaling, a physical control channeldedicated for CC assignment control information may be used, or a PDSCHconfigured in the form of L2 MAC message may be used.

FIG. 6 is a conceptual diagram illustrating downlink (DL) and uplink(UL) component carriers (CCs). Referring to FIG. 6, DL and UL CCs may beassigned from an eNB (cell) or RN. For example, the number of DL CCs maybe set to N and the number of UL CCs may be set to M.

Through the UE's initial access or initial deployment process, after RRCconnection is established on the basis of one certain CC for DL or UL(cell search) (for example, system information acquisition/reception,initial random access process, etc.), a unique carrier setup for each UEmay be provided from a dedicated signaling (UE-specific RRC signaling orUE-specific L1/L2 PDCCH signaling). For example, assuming that a carriersetup for UE is commonly achieved in units of an eNB (cell orcell-cluster), the UE carrier setup may also be provided throughcell-specific RRC signaling or cell-specific UE-common L1/L2 PDCCHsignaling. In another example, carrier component information for use inan eNB may be signaled to a UE through system information for RRCconnection setup, or may also be signaled to additional systeminformation or cell-specific RRC signaling upon completion of the RRCconnection setup.

While DL/UL CC setup has been described, centering on the relationshipbetween an eNB and a UE, to which the present invention is not limited,an RN may also provide DL/UL CC setup to a UE contained in an RN region.In addition, in association with a RN contained in an eNB region, theeNB may also provide DL/UL CC setup of the corresponding RN to the RN ofthe eNB region. For clarity, while the following description willdisclose DL/UL CC setup on the basis of the relationship between the eNBand the UE, it should be noted that the same content may also be appliedto the relationship between the RN and the UE (i.e., an access uplinkand downlink) or the relation between the eNB and the RN (backhauluplink or downlink) without departing from the scope or spirit of thepresent invention.

When the above-mentioned DL/UL CCs are uniquely assigned to individualUEs, DL/UL CC linkage may be implicitly or explicitly configured througha certain signaling parameter definition.

FIG. 7 shows an exemplary linkage of DL/UL CCs. In more detail, when aneNB configures two DL CCs (DL CC #a and DL CC #b) and two UL CCs (UL CC#i and UL CC #j), FIG. 6 shows a DL/UL CC linkage defined when two DLCCs (DL CC #a and DL CC #b) and one UL CC (UL CC #i) are assigned to acertain UE.

In a DL/UL CC linkage setup shown in FIG. 7, a solid line indicates alinkage setup between DL CC and UL CC that are basically constructed byan eNB, and this linkage setup between DL CC and UL CC may be defined in“System Information Block (SIB) 2”. In the DL/UL CC linkage setup shownin FIG. 7, a dotted line indicates a linkage setup between DL CC and ULCC configured in a specific UE. The above-mentioned DL CC and UL CClinkage setup shown in FIG. 7 is disclosed only for illustrativepurposes, and the scope or spirit of the present invention is notlimited thereto. That is, in accordance with various embodiments of thepresent invention, the number of DL CCs or UL CCs configured by eNB maybe set to an arbitrary number. Thus, the number of UE-specific DL CCs orthe number of UE-specific UL CCs in the above-mentioned DL CCs or UL CCsmay be set to an arbitrary number, and associated DL/UL CC linkage maybe defined in a different way from that of FIG. 7.

Further, from among DL CCs and UL CCs configured or assigned, a primaryCC (PCC), or a primary cell (P-cell) or an anchor CC (also called ananchor cell) may be configured. For example, a DL PCC (or DL P-cell)aiming to transmit configuration/reconfiguration information on RRCconnection setup may be configured. In another example, UL CC fortransmitting PUCCH to be used when a certain UE transmits UCI that mustbe transmitted on uplink may be configured as UL PCC (or UL P-cell). Forconvenience of description, it is assumed that one DL PCC (P-cell) andone UL PCC (P-cell) are basically assigned to each UE. Alternatively, ifa large number of CCs is assigned to UE or if CCs can be assigned from aplurality of eNBs, one or more DL PCCs (P-cells) and/or one or more ULPCCs (P-cells) may be assigned from one or more eNBs to a certain UE.For the linkage between DL PCC (P-cell) and UL PCC (P-cell), aUE-specific configuration method may be considered by eNB as necessary.To implement a more simplified method, a linkage between DL PCC (P-cell)and UL PCC (P-cell) may be configured on the basis of the relationshipof basic linkage that has been defined in LTE Release-8 (LTE Rel-8) andsignaled to System Information Block (or Base) 2. DL PCC (P-cell) and ULPCC (P-cell) for the above-mentioned linkage configuration are groupedso that the grouped result may be denoted by a UE-specific P-cell.

SC-FDMA Transmission and OFDMA Transmission

FIG. 8 is a conceptual diagram illustrating an SC-FDMA transmissionscheme and an OFDMA transmission scheme for use in a mobilecommunication system. The SC-FDMA transmission scheme may be used for ULtransmission and the OFDMA transmission scheme may be used for DLtransmission.

Each of the UL signal transmission entity (e.g., UE) and the DL signaltransmission entity (e.g., eNB) may include a Serial-to-Parallel (S/P)Converter 801, a subcarrier mapper 803, an M-point Inverse DiscreteFourier Transform (IDFT) module 804, and a Parallel-to-Serial Converter805. Each input signal that is input to the S/P converter 801 may be achannel coded and modulated data symbol. However, a user equipment (UE)for transmitting signals according to the SC-FDMA scheme may furtherinclude an N-point Discrete Fourier Transform (DFT) module 802. Theinfluence of IDFT processing of the M-point IDFT module 804 isconsiderably offset, such that a transmission signal may be designed tohave single carrier property. That is, the DFT module 802 performs DFTspreading of an input data symbol such that single carrier propertyrequisite for UL transmission may be satisfied. The SC-FDMA transmissionscheme basically provides good or superior Peak to Average Power ratio(PAPR) or Cubic Metric (CM), such that the UL transmitter can moreeffectively transmit data or information even in the case of the powerlimitation situation, resulting in an increase in user throughput.

FIG. 9 is a conceptual diagram illustrating maximum transmission powerfor single antenna transmission and MIMO transmission. FIG. 9( a) showsthe case of single antenna transmission. As can be seen from FIG. 9( a),one power amplifier (PA) may be provided to one antenna. In FIG. 9( a),an output signal (P_(max)) of the power amplifier (PA) may have aspecific value, for example, 23 dBm. In contrast, FIGS. 9( b) and 9(c)show the case of MIMO transmission. As can be seen from FIGS. 9( b) and9(c), several PAs may be mapped to respective transmission (Tx)antennas. For example, provided that the number of transmission (Tx)antennas is set to 2, 2 PAs may be mapped to respective transmission(Tx) antennas. The setting of output values (i.e., maximum transmissionpower) of 2 PAs may be configured in different ways as shown in FIGS. 9(b) and 9(c).

In FIG. 9( b), maximum transmission power (P_(max)) for single antennatransmission may be divisionally applied to PA1 and PA2. That is, if atransmission power value of x [dBm] is assigned to PA1, a transmissionpower value of (P_(max)−x) [dBm] may be applied to PA2. In this case,since total transmission power (P_(max)) is maintained, the transmittermay have higher robustness against the increasing PAPR in the powerlimitation situation.

On the other hand, as can be seen from FIG. 9( c), only one Tx antenna(ANT1) may have a maximum transmission power value (P_(max)), and theother Tx antenna (ANT2) may have a half value (P_(max)/2) of the maximumtransmission power value (P_(max)). In this case, only one transmissionantenna may have higher robustness against the increasing PAPR.

MIMO System

MIMO technology is not dependent on one antenna path to receive onetotal message, collects a plurality of data pieces received via severalantennas, and completes total data. As a result, MIMO technology canincrease a data transfer rate within a specific range, or can increase asystem range at a specific data transfer rate. Under this situation,MIMO technology is a next-generation mobile communication technologycapable of being widely applied to mobile communication terminals orRNs. MIMO technology can extend the range of data communication, so thatit can overcome the limited amount of transmission (Tx) data of mobilecommunication systems reaching a critical situation.

FIG. 10( a) is a block diagram illustrating a general MIMO communicationsystem. Referring to FIG. 10( a), if the number of transmission (Tx)antennas increases to N_(t), and at the same time the number ofreception (Rx) antennas increases to N_(R), a theoretical channeltransmission capacity of the MIMO communication system increases inproportion to the number of antennas, differently from theabove-mentioned case in which only a transmitter or receiver usesseveral antennas, so that a transfer rate and a frequency efficiency canbe greatly increased. In this case, the transfer rate acquired by theincreasing channel transmission capacity can theoretically increase by apredetermined amount that corresponds to multiplication of a maximumtransfer rate (R_(o)) acquired when one antenna is used and a rate ofincrease (R_(i)). The rate of increase (R_(i)) can be represented by thefollowing equation 1.

R=min(N _(T) ,N _(R))  [Equation 1]

For example, provided that a MIMO system uses four transmission (Tx)antennas and four reception (Rx) antennas, the MIMO system cantheoretically acquire a high transfer rate which is four times higherthan that of a one antenna system. After the above-mentioned theoreticalcapacity increase of the MIMO system was demonstrated in the mid-1990s,many developers began to conduct intensive research into a variety oftechnologies which can substantially increase a data transfer rate usingthe theoretical capacity increase. Some of the above technologies havebeen reflected in a variety of wireless communication standards, forexample, a third-generation mobile communication or a next-generationwireless LAN, etc.

A variety of MIMO-associated technologies have been intensivelyresearched by many companies or developers, for example, research intoan information theory associated with a MIMO communication capacitycalculation under various channel environments or multiple accessenvironments, research into a radio frequency (RF) channel measurementand modeling of the MIMO system, and research into a space-time signalprocessing technology.

A mathematical modeling of a communication method for use in theabove-mentioned MIMO system will hereinafter be described in detail. Ascan be seen from FIG. 10( a), it is assumed that there are N_(T)transmission (Tx) antennas and N_(R) reception (Rx) antennas. In thecase of a transmission (Tx) signal, a maximum number of transmissioninformation pieces is N_(T) under the condition that N_(T) transmission(Tx) antennas are used, so that the transmission (Tx) information can berepresented by a specific vector shown in the following equation 2.

s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

In the meantime, individual transmission (Tx) information pieces (s₁,s₂, . . . , s_(NT)) may have different transmission powers. In thiscase, if the individual transmission powers are denoted by (P₁, P₂, . .. , P_(NT)), transmission (Tx) information having an adjustedtransmission power can be represented by a specific vector shown in thefollowing equation 3.

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

In Equation 3, ŝ is a transmission vector, and can be represented by thefollowing equation 4 using a diagonal matrix P of a transmission (Tx)power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the meantime, the information vector ŝ having an adjustedtransmission power is applied to a weight matrix (W), so that N_(T)transmission (Tx) signals (x₁, x₂, . . . , x_(NT)) to be actuallytransmitted are configured. In this case, the weight matrix (W) isadapted to properly distribute transmission (Tx) information toindividual antennas according to transmission channel situations. Theabove-mentioned transmission (Tx) signals (x₁, x₂, . . . , x_(NT)) canbe represented by the following equation 5 using the vector (X).

$\begin{matrix}{x = {\quad{\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Next, if N_(R) reception (Rx) antennas are used, reception (Rx) signals(y₁, y₂, . . . , y_(NR)) of individual antennas can be represented by aspecific vector (y) shown in the following equation 6.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

In the meantime, if a channel modeling is executed in the MIMOcommunication system, individual channels can be distinguished from eachother according to transmission/reception (Tx/Rx) antenna indexes. Aspecific channel passing the range from a transmission (Tx) antenna (j)to a reception (Rx) antenna (i) is denoted by h_(ij). In this case, itshould be noted that the index order of the channel h_(ij) is locatedbefore a reception (Rx) antenna index and is located after atransmission (Tx) antenna index.

Several channels are tied up, so that they are displayed in the form ofa vector or matrix. An exemplary vector is as follows. FIG. 10( b) showschannels from N_(T) transmission (Tx) antennas to a reception (Rx)antenna (i).

Referring to FIG. 10( b), the channels passing the range from the N_(T)transmission (Tx) antennas to the reception (Rx) antenna (i) can berepresented by the following equation 7.

h _(i) ^(T) =└h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ┘  [Equation 7]

If all channels passing the range from the N_(T) transmission (Tx)antennas to N_(R) reception (Rx) antennas are denoted by the matrixshown in Equation 7, the following equation 8 is acquired.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 12} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Additive white Gaussian noise (AWGN) is added to an actual channel whichhas passed the channel matrix (H) shown in Equation 8. The AWGN (n₁, n₂,. . . , n_(NR)) added to each of N_(R) reception (Rx) antennas can berepresented by a specific vector shown in the following equation 9.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

A reception signal calculated by the above-mentioned equations can berepresented by the following equation 10.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

In the meantime, the number of rows and the number of columns of achannel matrix H indicating a channel condition are determined by thenumber of Tx/Rx antennas. In the channel matrix H, the number of rows isequal to the number (N_(R)) of Rx antennas, and the number of columns isequal to the number (N_(T)) of Tx antennas. Namely, the channel matrix His denoted by N_(R)×N_(T) matrix. Generally, a matrix rank is defined bya smaller number between the number of rows and the number of columns,in which the rows and the columns are independent of each other.Therefore, the matrix rank cannot be higher than the number of rows orcolumns. The rank of the channel matrix H can be represented by thefollowing equation 11.

rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

A variety of MIMO transmission/reception (Tx/Rx) schemes may be used foroperating the MIMO system, for example, frequency switched transmitdiversity (FSTD), Space Frequency Block Code (SFBC), Space Time BlockCode (STBC), Cyclic Delay Diversity (CDD), time switched transmitdiversity (TSTD), etc. In case of Rank 2 or higher, Spatial Multiplexing(SM), Generalized Cyclic Delay Diversity (GCDD), Selective VirtualAntenna Permutation (S-VAP), etc. may be used.

The FSTD scheme is to allocate subcarriers having different frequenciesto signals transmitted through multiple antennas so as to obtaindiversity gain. The SFBC scheme is to efficiently apply selectivity of aspatial region and a frequency region so as to obtain diversity gain andmultiuser scheduling gain. The STBC scheme is to apply selectivity of aspatial domain and a time region. The CDD scheme is to obtain diversitygain using path delay between transmission antennas. The TSTD scheme isto temporally divide signals transmitted through multiple antennas. Thespatial multiplexing scheme is to transmit different data throughantennas so as to increase a transfer rate. The GCDD scheme is to applyselectivity of a time region and a frequency region. The S-VAP schemeuses a single precoding matrix and includes a Multi Codeword (MCW)S-VAPfor mixing multiple codewords among antennas in spatial diversity orspatial multiplexing and a Single Codeword (SCW)S-VAP using a singlecodeword.

In case of the STBC scheme from among the above-mentioned MIMOtransmission schemes, the same data symbol is repeated to supportorthogonality in a time domain so that time diversity can be obtained.Similarly, the SFBC scheme enables the same data symbol to be repeatedto support orthogonality in a frequency domain so that frequencydiversity can be obtained. An exemplary time block code used for STBCand an exemplary frequency block code used for SFBC are shown inEquation 12 and Equation 13, respectively. Equation 12 shows a blockcode of the case of 2 transmission (Tx) antennas, and Equation 13 showsa block code of the case of 4 transmission (Tx) antennas.

$\begin{matrix}{\frac{1}{\sqrt{2}}\begin{pmatrix}S_{1} & S_{2} \\{- S_{2}^{*}} & S_{1}^{*}\end{pmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack \\{\frac{1}{\sqrt{2}}\begin{pmatrix}S_{1} & S_{2} & 0 & 0 \\0 & 0 & S_{3} & S_{4} \\{- S_{2}^{*}} & S_{1}^{*} & 0 & 0 \\0 & 0 & {- S_{4}^{*}} & S_{3}^{*}\end{pmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Equations 12 and 13, S_(i) (i=1, 2, 3, 4) means a modulated datasymbol. In addition, each row of the matrixes of Equation 12 and 13 mayindicate an antenna port, and each column may indicate time (in case ofSTBC) or frequency (in case of SFBC).

On the other hand, the CDD scheme from among the above-mentioned MIMOtransmission schemes mandatorily increases delay spread so as toincrease frequency diversity. FIG. 11 is a conceptual diagramillustrating a general CDD structure for use in the MIMO system. FIG.11( a) shows a method for applying cyclic delay to a time domain. Ifnecessary, the CDD scheme based on the cyclic delay of FIG. 11( a) mayalso be implemented as phase-shift diversity of FIG. 11( b).

In association with the above-mentioned MIMO transmission techniques,the codebook-based precoding method will hereinafter be described withreference to FIG. 12. FIG. 12 is a conceptual diagram illustratingcodebook-based precoding.

In accordance with the codebook-based precoding scheme, a transceivermay share codebook information including a predetermined number ofprecoding matrixes according to a transmission rank, the number ofantennas, etc. That is, if feedback information is infinite, theprecoding-based codebook scheme may be used. The receiver measures achannel status through a reception signal, so that an infinite number ofpreferred precoding matrix information (i.e., an index of thecorresponding precoding matrix) may be fed back to the transmitter onthe basis of the above-mentioned codebook information. For example, thereceiver may select an optimum precoding matrix by measuring an ML(Maximum Likelihood) or MMSE (Minimum Mean Square Error) scheme.Although the receiver shown in FIG. 12 transmits precoding matrixinformation for each codeword to the transmitter, the scope or spirit ofthe present invention is not limited thereto.

Upon receiving feedback information from the receiver, the transmittermay select a specific precoding matrix from a codebook on the basis ofthe received information. The transmitter that has selected theprecoding matrix performs a precoding operation by multiplying theselected precoding matrix by as many layer signals as the number oftransmission ranks, and may transmit each precoded Tx signal over aplurality of antennas. If the receiver receives the precoded signal fromthe transmitter as an input, it performs inverse processing of theprecoding having been conducted in the transmitter so that it canrecover the reception (Rx) signal. Generally, the precoding matrixsatisfies a unitary matrix (U) such as (U*U^(H)=I), so that the inverseprocessing of the above-mentioned precoding may be conducted bymultiplying a Hermit matrix (PH) of the precoding matrix H used in theprecoding of the transmitter by the reception (Rx) signal.

Physical Uplink Control Channel (PUCCH)

PUCCH including UL control information will hereinafter be described indetail.

A plurality of UE control information pieces may be transmitted througha PUCCH. When Code Division Multiplexing (CDM) is performed in order todiscriminate signals of UEs, a Constant Amplitude Zero Autocorrelation(CAZAC) sequence having a length of 12 is mainly used. Since the CAZACsequence has a property that a constant amplitude is maintained in atime domain and a frequency domain, a Peak-to-Average Power Ratio (PAPR)of a UE or Cubic Metic (CM) may be decreased to increase coverage. Inaddition, ACK/NACK information for DL data transmitted through the PUCCHmay be covered using an orthogonal sequence.

In addition, control information transmitted through the PUCCH may bediscriminated using cyclically shifted sequences having different cyclicshift values. A cyclically shifted sequence may be generated bycyclically shifting a basic sequence (also called a base sequence) by aspecific cyclic shift (CS) amount. The specific CS amount is indicatedby a CS index. The number of available CSs may be changed according tochannel delay spread. Various sequences may be used as the basicsequence and examples thereof include the above-described CAZACsequence.

PUCCH may include a variety of control information, for example, aScheduling Request (SR), DL channel measurement information, andACK/NACK information for DL data transmission. The channel measurementinformation may include a Channel Quality Indicator (CQI), a PrecodingMatrix Index (PMI), and a Rank Indicator (RI).

PUCCH format may be defined according to the type of control informationcontained in a PUCCH, modulation scheme information thereof, etc. Thatis, PUCCH format 1 may be used for SR transmission, PUCCH format 1a or1b may be used for HARQ ACK/NACK transmission, PUCCH format 2 may beused for CQI transmission, and PUCCH format 2a/2b may be used for HARQACK/NACK transmission.

If HARQ ACK/NACK is transmitted alone in an arbitrary subframe, PUCCHformat 1a or 1b may be used. If SR is transmitted alone, PUCCH format 1may be used. The UE may transmit the HARQ ACK/NACK and the SR throughthe same subframe, and a detailed description thereof will hereinafterbe described in detail.

PUCCH format may be summarized as shown in Table 1.

TABLE 1 Number of PUCCH Modulation bits per format scheme subframe Usageetc. 1 N/A N/A SR (Scheduling Request) 1a BPSK  1 ACK/NACK One codeword1b QPSK  2 ACK/NACK Two codeword 2 QPSK 20 CQI Joint Coding ACK/NACK(extended CP) 2a QPSK + 21 CQI + ACK/NACK Normal CP BPSK only 2b QPSK +22 CQI + ACK/NACK Normal CP BPSK only

FIG. 13 shows a PUCCH resource mapping structure for use in a ULphysical resource block (PRB). N_(RB) ^(UL) is the number of resourceblocks (RBs) for use in uplink (UL), and nPRB is a physical resourceblock (PRB) number. PUCCH may be mapped to both edges of a UL frequencyblock. CQI resources may be mapped to a PRB located just after the edgeof a frequency band, and ACK/NACK may be mapped to this PRB.

PUCCH format 1 may be a control channel used for SR transmission. SR(Scheduling Request) may be transmitted in such a manner that SR isrequested or not requested.

PUCCH format 1a/1b is a control channel used for ACK/NACK transmission.In the PUCCH format 1a/1b, a symbol modulated using the BPSK or QPSKmodulation scheme is multiplied by a CAZAC sequence of the length 12.Upon completion of the CAZAC sequence multiplication, the resultantsymbol is blockwise-spread as an orthogonal sequence. A Hadamardsequence of the length 4 is applied to general ACK/NACK information, anda DFT (Discrete Fourier Transform) sequence of the length 3 is appliedto the shortened ACK/NACK information and a reference signal. A Hadamardsequence of the length 2 may be applied to the reference signal for theextended CP.

The UE may also transmit HARQ ACK/NACK and SR through the same subframe.For positive SR transmission, the UE may transmit HARQ ACK/NACKinformation through resources allocated for the SR. For negative SRtransmission, the UE may transmit HARQ ACK/NACK information throughresources allocated for ACK/NACK information.

PUCCH format 2/2a/2b will hereinafter be described in detail. PUCCHformat 2/2a/2b is a control channel for transmitting channel measurementfeedback (CQI, PMI, RI).

The PUCCH format 2/2a/2b may support modulation based on a CAZACsequence, and a QPSK-modulated symbol may be multiplied by a CAZACsequence of the length 12. Cyclic shift (CS) of the sequence may bechanged between a symbol and a slot. For a reference signal (RS),orthogonal covering may be used.

FIG. 14 shows a channel structure of a CQI information bit. The CQI bitmay include one or more fields. For example, the CQI bit may include aCQI field indicating a CQI index for MCS decision, a PMI fieldindicating an index of a precoding matrix of a codebook, and an RI fieldindicating a rank.

Referring to FIG. 14( a), a reference signal (RS) may be loaded on twoSC-FDMA symbols spaced apart from each other by a predetermined distancecorresponding to 3 SC-FDMA symbol intervals from among 7 SC-FDMA symbolscontained in one slot, and CQI information may be loaded on theremaining 5 SC-FDMA symbols. The reason why two RSs may be used in oneslot is to support a high-speed UE. In addition, each UE may bediscriminated by a sequence. CQI symbols may be modulated in the entireSC-FDMA symbol, and the modulated CQI symbols are transmitted. TheSC-FDMA symbol is composed of one sequence. That is, a UE performs CQImodulation using each sequence, and transmits the modulated result.

The number of symbols that can be transmitted to one TTI is set to 10,and CQI modulation is extended up to QPSK. If QPSK mapping is applied tothe SC-FDMA symbol, a CQI value of 2 bits may be loaded on the SC-FDMAsymbol, so that a CQI value of 10 bits may be assigned to one slot.Therefore, a maximum of 20-bit CQI value may be assigned to onesubframe. A frequency domain spreading code may be used to spread CQI ina frequency domain.

CAZAC sequence (for example, a ZC sequence) may be used as a frequencydomain spread code. In addition, another sequence having superiorcorrelation characteristics may be used as the frequency domain spreadcode. Specifically, CAZAC sequences having different cyclic shift (CS)values may be applied to respective control channels, such that theCAZAC sequences may be distinguished from one another. IFFT may beapplied to the frequency domain spread CQI.

FIG. 14( b) shows the example of PUCCH format 2/2a/2b transmission incase of the extended CP. One slot includes 6 SC-FDMA symbols. RS isassigned to one OFDM symbol from among 6 OFDM symbols of each slot, anda CQI bit may be assigned to the remaining 5 OFDM symbols. Except forthe six SC-FDMA symbols, the example of the normal CP of FIG. 14( a) maybe used without change.

Orthogonal covering applied to the RS of FIGS. 14( a) and 14(b) is shownin Table 2.

TABLE 2 Normal CP Extended CP [1 1] [1]

Simultaneous transmission of CQI and ACK/NACK information willhereinafter be described with reference to FIG. 15.

In case of the normal CP, CQI and ACK/NACK information can besimultaneously transmitted using PUCCH format 2a/2b. ACK/NACKinformation may be transmitted through a symbol where CQI RS istransmitted. That is, a second RS for use in the normal CP may bemodulated into an ACK/NACK symbol. In the case where the ACK/NACK symbolis modulated using the BPSK scheme as shown in the PUCCH format 1a, CQIRS may be modulated into the ACK/NACK symbol according to the BPSKscheme. In the case where the ACK/NACK symbol is modulated using theQPSK scheme as shown in the PUCCH format 1 b, CQI RS may be modulatedinto the ACK/NACK symbol according to the QPSK scheme. On the otherhand, in case of the extended CP, CQI and ACK/NACK information aresimultaneously transmitted using the PUCCH format 2. For this purpose,CQI and ACK/NACK information may be joint-coded.

For details of PUCCH other than the above-mentioned description, the3GPP standard document (e.g., 3GPP TS36.211 5.4) may be referred to, anddetailed description thereof will herein be omitted for convenience ofdescription. However, it should be noted that PUCCH contents disclosedin the above-mentioned standard document can also be applied to a PUCCHused in various embodiments of the present invention without departingfrom the scope or spirit of the present invention.

Channel Status Information (CSI) Feedback

In order to correctly perform MIMO technology, the receiver may feedback a rank indicator (RI), a precoding matrix index (PMI) and a channelquality indicator (CQI) to the transmitter. RI, PMI and CQI may begenerically named Channel Status Information (CSI) as necessary.Alternatively, the term “CQI” may be used as the concept of channelinformation including RI, PMI and CQI.

FIG. 16 is a conceptual diagram illustrating a feedback of channelstatus information.

Referring to FIG. 16, MIMO transmission data from the transmitter may bereceived at a receiver over a channel (H). The receiver may select apreferred precoding matrix from a codebook on the basis of the receivedsignal, and may feed back the selected PMI to the transmitter. Inaddition, the receiver may measure a Signal-to-Interference plus NoiseRatio (SINR) of the reception (Rx) signal, calculate channel qualityinformation (CQI), and feed back the calculated CQI to the transmitter.In addition, the receiver may measure a Signal-to-Interference plusNoise Ratio (SINR) of the reception (Rx) signal, calculate a CQI, andfeed back the calculated SINR to the transmitter. In addition, thereceiver may feed back a rank indicator (RI) of the Rx signal to thetransmitter. The transmitter may determine the number of layers suitablefor data transmission to the receiver and time/frequency resources, MCS(Modulation and Coding Scheme), etc. using RI and CQI information fedback from the receiver. In addition, the receiver may transmit theprecoded Tx signal using the precoding matrix (W_(I)) indicated by a PMIfed back from the receiver over a plurality of antennas.

Channel status information will hereinafter be described in detail.

RI is information regarding a channel rank (i.e., the number of layersfor data transmission of a transmitter). RI may be determined by thenumber of allocated Tx layers, and may be acquired from associateddownlink control information (DCI).

PMI is information regarding a precoding matrix used for datatransmission of a transmitter. The precoding matrix fed back from thereceiver may be determined considering the number of layers indicated byRI. PMI may be fed back in case of a closed-loop spatial multiplexing(SM) and a large delay cyclic delay diversity (CDD). In the case of anopen-loop transmission, the transmitter may select a precoding matrixaccording to the predetermined rules. A process for selecting a PMI foreach rank (rank 1 to 4) is as follows. The receiver may calculate anpost processing SINR in each PMI, convert the calculated SINR into thesum capacity, and select the best PMI on the basis of the sum capacity.That is, PMI calculation of the receiver may be considered to be aprocess for searching for an optimum PMI on the basis of the sumcapacity. The transmitter that has received PMI feedback from thereceiver may use a precoding matrix recommended by the receiver. Thisfact may be contained as 1-bit indicator in scheduling allocationinformation for data transmission to the receiver. Alternatively, thetransmitter may not use the precoding matrix indicated by a PMI fed backfrom the transmitter. In this case, precoding matrix information usedfor data transmission from the transmitter to the receiver may beexplicitly contained in the scheduling allocation information. Fordetails of PMI, the 3GPP standard document (e.g., 3GPP TS36.211) may bereferred to.

CQI is information regarding a channel quality. CQI may be representedby a predetermined MCS combination. CQI index may be given as shown inthe following table 3.

TABLE 3 CQI index modulation code rate x 1024 efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 12 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

Referring to Table 3, CQI index may be represented by 4 bits (i.e., CQIindexes of 0˜15). Each CQI index may indicate a modulation scheme and acode rate.

A CQI calculation method will hereinafter be described. The followingassumptions (1) to (5) for allowing a UE to calculate a CQI index aredefined in the 3GPP standard document (e.g., 3GPP TS36.213).

(1) First three OFDM symbols in one subframe are occupied by controlsignaling.

(2) Resource element (RE) used by a primary synchronization signal, asecondary synchronization signal or a physical broadcast channel (PBCH)is not present.

(3) CP length of a non-MBSFN subframe is assumed.

(4) Redundancy version is set to zero (0).

(5) PDSCH transmission method may be dependent upon a currentlytransmission mode (e.g., a default mode) configured in a UE.

(6) The ratio of PDSCH EPRE (Energy Per Resource Element) to acell-specific reference signal EPRE may be given with the exception ofρ_(A). (A detailed description of ρ_(A) may follow the followingassumption. Provided that a UE for an arbitrary modulation scheme may beset to a Transmission Mode 2 having four cell-specific antenna ports ormay be set to a Transmission Mode 3 having an RI of 1 and fourcell-specific antenna ports, ρ_(A) may be denoted byρ_(A)=P_(A)+Δ_(offset)+10 log₁₀ (2) [dB]. In the remaining cases, inassociation with an arbitrary modulation method and the number ofarbitrary layers, ρ_(A) may be denoted by ρ_(A)=P_(A)+Δ_(offset) [dB].Δ_(offset) is given by a nomPDSCH-RS-EPRE-Offset parameter configured byhigher layer signaling.)

Definition of the above-mentioned assumptions (1) to (5) may indicatethat a CQI includes not only a CQI but also various information of acorresponding UE. That is, different CQI indexes may be fed backaccording to a throughput or performance of the corresponding UE at thesame channel quality, so that it is necessary to define a predeterminedreference for the above-mentioned assumption.

The UE may receive a downlink reference signal (DL RS) from an eNB, andrecognize a channel status on the basis of the received DL RS. In thiscase, the RS may be a common reference signal (CRS) defined in thelegacy 3GPP LTE system, and may be a Channel Status InformationReference Signal (CSI-RS) defined in a system (e.g., 3GPP LTE-A system)having an extended antenna structure. The UE may satisfy the assumptiongiven for CQI calculation at a channel recognized through a referencesignal (RS), and at the same time calculate a CQI index in which a BlockError Rate (BLER) is not higher than 10%. The UE may transmit thecalculated CQI index to the eNB. The UE may not apply a method forimproving interference estimation to a CQI index calculation process.

The process for allowing the UE to recognize a channel status andcalculate an appropriate MCS may be defined in various ways in terms ofUE implementation. For example, the UE may calculate a channel status oran effective SINR using a reference signal (RS). In addition, thechannel status or the effective SINR may be measured on the entiresystem bandwidth (also called ‘Set S’) or may also be measured on somebandwidths (specific subband or specific RB). The CQI for the set S maybe referred to as a Wideband WB CQI, and the CQI for some bandwidths maybe referred to as a subband (SB) CQI. The UE may calculate the highestMCS on the basis of the calculated channel status or effective SINR. Thehighest MCS may indicate an MCS that satisfies the CQI calculationassumption without exceeding a transport block error rate of 10% duringthe decoding. The UE may determine a CQI index related to the calculatedMCS, and may report the determined CQI index to the eNB.

Further, CQI-only transmission may be considered in which a UE transmitsonly a CQI. Aperiodic CQI transmission may be event-triggered uponreceiving a request from the eNB. Such request from the eNB may be a CQIrequest defined by one bit on DCI format 0. In addition, for CQI-onlytransmission, MCS index (I_(MCS)) of 29 may be signaled as shown in thefollowing table 4. In this case, the CQI request bit of the DCI format 0is set to 1, transmission of 4 RBs or less may be configured, RedundancyVersion 1 (RV1) is indicated in PUSCH data retransmission, and amodulation order (Q_(m)) may be set to 2. In other words, in the case ofCQI-only transmission, only a QPSK (Quadrature Phase Shift Keying)scheme may be used as a modulation scheme.

TABLE 4 Modulation TBS Redundancy MCS Index Order Index Version I_(MCS)Q′_(m) I_(TBS) rv_(idx) 0 2 0 0 1 2 1 0 2 2 2 0 3 2 3 0 4 2 4 0 5 2 5 06 2 6 0 7 2 7 0 8 2 8 0 9 2 9 0 10 2 10 0 11 4 10 0 12 4 11 0 13 4 12 014 4 13 0 15 4 14 0 16 4 15 0 17 4 16 0 18 4 17 0 19 4 18 0 20 4 19 0 216 19 0 22 6 20 0 23 6 21 0 24 6 22 0 25 6 23 0 26 6 24 0 27 6 25 0 28 626 0 29 reserved 1 30 2 31 3

The CQI reporting operation will hereinafter be described in detail.

In the 3GPP LTE system, when a DL reception entity (e.g., UE) is coupledto a DL transmission entity (e.g., eNB), a Reference Signal ReceivedPower (RSRP) and a Reference Signal Received Quality (RSRQ) that aretransmitted via downlink are measured at an arbitrary time, and themeasured result may be periodically or event-triggeredly reported to theeNB.

In a cellular OFDM wireless packet communication system, each UE mayreport DL channel information based on a DL channel condition viauplink, and the eNB may determine time/frequency resources and MCS(Modulation and Coding Scheme) so as to transmit data to each UE usingDL channel information received from each UE.

In case of the legacy 3GPP LTE system (e.g., 3GPP LTE Release-8 system),such channel information may be composed of Channel Quality Indication(CQI), Precoding Matrix Indicator (PMI), and Rank Indication (RI). Allor some of CQI, PMI and RI may be transmitted according to atransmission mode of each UE. CQI may be determined by the receivedsignal quality of the UE. Generally, CQI may be determined on the basisof DL RS measurement. In this case, a CQI value actually applied to theeNB may correspond to an MCS in which the UE maintains a Block ErrorRate (BLER) of 10% or less at the measured Rx signal quality and at thesame time has a maximum throughput or performance. In addition, suchchannel information reporting scheme may be divided into periodicreporting and aperiodic reporting upon receiving a request from the eNB.

Information regarding the aperiodic reporting may be assigned to each UEby a CQI request field of 1 bit contained in uplink schedulinginformation sent from the eNB to the UE. Upon receiving the aperiodicreporting information, each UE may transmit channel informationconsidering the UE's transmission mode to the eNB over a physical uplinkshared channel (PUSCH). If necessary, RI and CQI/PMI may not betransmitted over the same PUSCH.

In case of the aperiodic reporting, a cycle in which channel informationis transmitted via an upper layer signal, an offset of the correspondingperiod, etc. may be signaled to each UE in units of a subframe, andchannel information considering a transmission (Tx) mode of each UE maybe transmitted to the eNB over a physical uplink control channel (PUCCH)at intervals of a predetermined time. In the case where UL transmissiondata is present in a subframe to which channel information istransmitted at intervals of a predetermined time, the correspondingchannel information may be transmitted together with data over not aPUCCH but a PUSCH together. In case of the periodic reporting over aPUCCH, a limited number of bits may be used as compared to PUSCH. RI andCQI/PMI may be transmitted over the same PUSCH. If the periodicreporting collides with the aperiodic reporting, only the aperiodicreporting may be performed within the same subframe.

In order to calculate a WB CQI/PMI, the latest transmission RI may beused. In a PUCCH reporting mode, RI may be independent of another RI foruse in a PUSCH reporting mode. RI may be effective only at CQI/PMI foruse in the corresponding PUSCH reporting mode.

The CQI/PMI/RI feedback type for the PUCCH reporting mode may beclassified into four feedback types (Type 1 to Type 4). Type 1 is a CQIfeedback for a user-selected subband. Type 2 is a WB CQI feedback and aWB PMI feedback. Type 3 is an RI feedback. Type 4 is a WB CQI feedback.

Referring to Table 5, in the case of periodic reporting of channelinformation, a reporting mode is classified into four reporting modes(Modes 1-0, 1-1, 2-0 and 2-1) according to CQI and PMI feedback types.

TABLE 5 PMI Feedback Type No PMI (OL, TD, single-antenna) Single PMI(CL) CQI Wideband Mode 1-0 Mode 1-1 Feedback RI (only for Open-Loop SM)RI Type One Wideband CQI (4 bit) Wideband CQI (4 bit) when RI > 1, CQIof first codeword Wideband spatial CQI (3 bit) for RI > 1 Wideband PMI(4 bit) UE Mode 2-0 Mode 2-1 Selected RI (only for Open-Loop SM) RIWideband CQI (4 bit) Wideband CQI (4 bit) Best-1 CQI (4 bit) in each BPWideband spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)Wideband PMI (4 bit) when RI > 1, CQI of first codeword Best-1 CQI (4bit) 1 in each BP Best-1 spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)

The reporting mode is classified into a wideband (WB) CQI and a subband(SB) CQI according to a CQI feedback type. The reporting mode isclassified into a No-PMI and a Single PMI according to transmission ornon-transmission of PMI. As can be seen from Table 5, ‘NO PMI’ maycorrespond to an exemplary case in which an Open Loop (OL), a TransmitDiversity (TD), and a single antenna are used, and ‘Single PMI” maycorrespond to an exemplary case in which a closed loop (CL) is used.

Mode 1-0 may indicate an exemplary case in which PMI is not transmittedbut WB CQI is transmitted only. In case of Mode 1-0, RI may betransmitted only in the case of Spatial Multiplexing (SM), and one WBCQI denoted by 4 bits may be transmitted. If RI is higher than ‘1’, aCQI for a first codeword may be transmitted. In case of Mode 1-0,Feedback Type 3 and Feedback Type 4 may be multiplexed at different timepoints within the predetermined reporting period, and then transmitted.The above-mentioned Mode 1-0 transmission scheme may be referred to asTime Division Multiplexing (TDM)-based channel information transmission.

Mode 1-1 may indicate an exemplary case in which a single PMI and a WBCQI are transmitted. In this case, 4-bit WB CQI and 4-bit WB PMI may betransmitted simultaneously with RI transmission. In addition, if RI ishigher than ‘1’, 3-bit WB Spatial Differential CQI may be transmitted.In case of transmission of two codewords, the WB spatial differentialCQI may indicate a differential value between a WB CQI index forCodeword 1 and a WB CQI index for Codeword 2. These differential valuesmay be assigned to the set {−4, −3, −2, −1, 0, 1, 2, 3}, and eachdifferential value may be assigned to any one of values contained in theset and be represented by 3 bits. In case of Mode 1-1, Feedback Type 2and Feedback Type 3 may be multiplexed at different time points withinthe predetermined reporting period, and then transmitted.

Mode 2-0 may indicate that no PMI is transmitted and a CQI of aUE-selected band is transmitted. In this case, RI may be transmittedonly in case of an open loop spatial multiplexing (OL SM) only, a WB CQIdenoted by 4 bits may be transmitted. In each Bandwidth Part (BP),Best-1 CQI may be transmitted, and Best-1 CQI may be denoted by 4 bits.In addition, an indicator of L bits indicating Best-1 may be furthertransmitted. If RI is higher than ‘1’, CQI for a first codeword may betransmitted. In case of Mode 2-0, the above-mentioned feedback type 1,feedback type 3, and feedback type 4 may be multiplexed at differenttime points within a predetermined reporting period, and thentransmitted.

Mode 2-1 may indicate an exemplary case in which a single PMI and a CQIof a UE-selected band are transmitted. In this case, WB CQI of 4 bits,WB spatial differential CQI of 3 bits, and WB PMI of 4 bits aretransmitted simultaneously with RI transmission. In addition, a Best-1CQI of 4 bits and a Best-1 indicator of L bits may be simultaneouslytransmitted at each bandwidth part (BP). If RI is higher than ‘1’, aBest-1 spatial differential CQI of 3 bits may be transmitted. Duringtransmission of two codewords, a differential value between a Best-1 CQIindex of Codeword 1 and a Best-1 CQI index of Codeword 2 may beindicated. In Mode 2-1, the above-mentioned feedback type 1, feedback 2,and feedback type 3 may be multiplexed at different time points within apredetermined reporting period, and then transmitted.

In the UE selected SB CQI reporting mode, the size of BP (BandwidthPart) subband may be defined by the following table 6.

TABLE 6 System Bandwidth Subband Size k Bandwidth Parts N_(RB) ^(DL)(RBs) (J) 6-7  NA NA 8-10 4 1 11-26  4 2 27-63  6 3 64-110 8 4

Table 6 shows a bandwidth part (BP) configuration and the subband sizeof each BP according to the size of a system bandwidth. UE may select apreferred subband within each BP, and calculate a CQI for thecorresponding subband. In Table 6, if the system bandwidth is set to 6or 7, this means no application of both the subband size and the numberof bandwidth parts (BPs). That is, the system bandwidth of 6 or 7 meansapplication of only WB CQI, no subband state, and a BP of 1.

FIG. 17 shows an example of a UE selected CQI reporting mode.

N_(RB) ^(DL) is the number of RBs of the entire bandwidth. The entirebandwidth may be divided into N CQI subbands (1, 2, 3, . . . , N). OneCQI subband may include k RBs defined in Table 6. If the number of RBsof the entire bandwidth is not denoted by an integer multiple of k, thenumber of RBs contained in the last CQI subband (i.e., the N-th CQIsubband) may be determined by the following equation 14.

N _(RB) ^(DL) −k·└N _(RB) ^(DL) /k┘  [Equation 14]

In Equation 14, └ ┘ represents a floor operation, and └x┘ or floor(x)represents a maximum integer not higher than ‘x’.

In addition, NJ CQI subbands construct one BP, and the entire bandwidthmay be divided into J BPs. UE may calculate a CQI index for onepreferred Best-1 CQI subband in contained in one BP, and transmit thecalculated CQI index over a PUCCH. In this case, a Best-1 indicatorindicating which a Best-1 CQI subband is selected in one BP may also betransmitted. The Best-1 indicator may be composed of L bits, and L maybe represented by the following equation 15.

L=┌log₂ N _(j)┐  [Equation 15]

In Equation 15, ┌ ┐ may represent a ceiling operation, and ┌x┐ orceiling(x) may represent a minimum integer not higher than ‘x’.

In the above-mentioned UE selected CQI reporting mode, a frequency bandfor CQI index calculation may be determined. Hereinafter, a CQItransmission cycle will hereinafter be described in detail.

Each UE may receive information composed of a combination of atransmission cycle of channel information and an offset from an upperlayer through RRC signaling. The UE may transmit channel information toan eNB on the basis of the received channel information transmissioncycle information.

FIG. 18 is a conceptual diagram illustrating a method for enabling a UEto periodically transmit channel information. For example, if a UEreceives combination information in which a channel informationtransmission cycle is set to 5 and an offset is set to 1, the UEtransmits channel information in units of 5 subframes, one subframeoffset is assigned in the increasing direction of a subframe index onthe basis of the Oth subframe, and channel information may be assignedover a PUCCH. In this case, the subframe index may be comprised of acombination of a system frame number (n_(f)) and 20 slot indexes (n_(s),0˜19) present in the system frame. One subframe may be comprised of 2slots, such that the subframe index may be represented by10×n_(f)+floor(n_(s)/2).

One type for transmitting only WB CQI and the other type fortransmitting both WB CQI and SB CQI may be classified according to CQIfeedback types. In case of the first type for transmitting only the WBCQI, WB CQI information for the entire band is transmitted at a subframecorresponding to each CQI transmission cycle. The WB periodic CQIfeedback transmission cycle may be set to any of 2, 5, 10, 16, 20, 32,40, 64, 80, or 160 ms or no transmission of the WB periodic CQI feedbacktransmission cycle may be established. In this case, if it is necessaryto transmit PMI according to the PMI feedback type of Table 5, PMIinformation is transmitted together with CQI. In case of the second typefor transmitting both WB CQI and SB CQI, WB CQI and SB CQI may bealternately transmitted.

FIG. 19 is a conceptual diagram illustrating a method for transmittingboth WB CQI and SB CQI according to an embodiment of the presentinvention. FIG. 19 shows an exemplary system comprised of 16 RBs. If asystem frequency band is comprised of 16 RBs, for example, it is assumedthat two bandwidth parts (BPs) (BP0 and BP1) may be configured, each BPmay be composed of 2 subbands (SBs) (SB0 and SB1), and each SB may becomposed of 4 RBs. In this case, as previously stated in Table 6, thenumber of BPs and the size of each SB are determined according to thenumber of RBs contained in the entire system band, and the number of SBscontained in each BP may be determined according to the number of RBs,the number of BPs and the size of SB.

In case of the type for transmitting both WB CQI and SB CQI, the WB CQIis transmitted to the CQI transmission subframe. In the nexttransmission subframe, a CQI of one SB (i.e., Best-1) having a goodchannel state from among SB0 and SB1 at BP0 and an index (i.e., Best-1indicator) of the corresponding SB are transmitted. In the further nexttransmission subframe, a CQI of one SB (i.e., Best-1) having a goodchannel state from among SB0 and SB1 at BP1 and an index (i.e., Best-1indicator) of the corresponding SB are transmitted. After transmittingthe WB CQI, CQIs of individual BPs are sequentially transmitted. In thiscase, CQI of a BP located between a first WB CQI transmitted once and asecond WB CQI to be transmitted after the first WB CQI may besequentially transmitted one to four times. For example, if the CQI ofeach BP is transmitted once during a time interval between two WB CQIs,CQIs may be transmitted in the order of WB CQI→BP0 CQI→BP1 CQI→WB CQI.In another example, if the CQI of each BP is transmitted four timesduring a time interval between two WB CQIs, CQIs may be transmitted inthe order of WB CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→BP0CQI→BP1 CQI→WB CQI. Information about the number of sequentialtransmission times of BP CQI during a time interval between two WB CQIsis signaled through a higher layer. Irrespective of WB CQI or SB CQI,the above-mentioned information about the number of sequentialtransmission times of BP CQI may be transmitted through a PUCCH in asubframe corresponding to information of a combination of channelinformation transmission cycle signaled from the higher layer of FIG. 18and an offset.

In this case, if PMI also needs to be transmitted according to the PMIfeedback type, PMI information and CQI must be simultaneouslytransmitted. If PUSCH for UL data transmission is present in thecorresponding subframe, CQI and PMI can be transmitted along with datathrough PUSCH instead of PUCCH.

FIG. 20 is a conceptual diagram illustrating an exemplary CQItransmission scheme when both WB CQI and SB CQI are transmitted. In moredetail, provided that combination information in which a channelinformation transmission cycle is set to 5 and an offset is set to 1 issignaled as shown in FIG. 18, and BP information between two WB CQI/PMIparts is sequentially transmitted once, FIG. 20 shows the example ofchannel information transmission operation of a UE.

On the other hand, in case of RI transmission, RI may be signaled byinformation of a combination of one signal indicating how many WBCQI/PMI transmission cycles are used for RI transmission and an offsetof the corresponding transmission cycle. In this case, the offset may bedefined as a relative offset for a CQI/PMI transmission offset. Forexample, provided that an offset of the CQI/PMI transmission cycle isset to 1 and an offset of the RI transmission cycle is set to zero, theoffset of the RI transmission cycle may be identical to that of theCQI/PMI transmission cycle. The offset of the RI transmission cycle maybe defined as a negative value or zero.

FIG. 21 is a conceptual diagram illustrating transmission of WB CQI, SBCQI and RI. In more detail, FIG. 21 shows that, under CQI/PMItransmission of FIG. 20, an RI transmission cycle is one time the WBCQI/PMI transmission cycle and the offset of RI transmission cycle isset to ‘−1’. Since the RI transmission cycle is one time the WB CQI/PMItransmission cycle, the RI transmission cycle has the same time cycle. Arelative difference between the RI offset value ‘−1’ and the CQI offset‘1’ of FIG. 20 is set to ‘−1’, such that RI can be transmitted on thebasis of the subframe index ‘0’.

In addition, provided that RI transmission overlaps with WB CQI/PMItransmission or SB CQI/PMI transmission, WB CQI/PMI or SB CQI/PMI maydrop. For example, provided that the RI offset is set to ‘0’ instead of‘−1’, the WB CQI/PMI transmission subframe overlaps with the RItransmission subframe. In this case, WB CQI/PMI may drop and RI may betransmitted.

By the above-mentioned combination, CQI, PMI, and RI may be transmitted,and such information may be transmitted from each UE by RRC signaling ofa higher layer. The BS (or eNB) may transmit appropriate information toeach UE in consideration of a channel situation of each UE and adistribution situation of UEs contained in the BS (or eNB).

Meanwhile, payload sizes of SB CQI, WB CQI/PMI, RI and WB CQI inassociation with the PUCCH report type may be represented by thefollowing table 7.

TABLE 7 PUCCH PUCCH Reporting Modes Report Mode 1-1 Mode 2-1 Mode 1-0Mode 2-0 Type Reported Mode State (bits/BP) (bits/BP) (bits/BP)(bits/BP) 1 Sub-band RI = 1 NA 4 + L NA 4 + L CQI RI > 1 NA 7 + L NA 4 +L 2 Wideband 2 TX Antennas RI = 1 6 6 NA NA CQI/PMI 4 TX Antennas RI = 18 8 NA NA 2 TX Antennas RI > 1 8 8 NA NA 4 TX Antennas RI > 1 11  11  NANA 3 RI 2-layer spatial multiplexing 1 1 1 1 4-layer spatialmultiplexing 2 2 2 2 4 Wideband RI = 1 or RI > 1 NA NA 4 4 CQI

Aperiodic transmission of CQI, PMI and RI over a PUSCH will hereinafterbe described.

In case of the aperiodic reporting, RI and CQI/PMI may be transmittedover the same PUSCH. In case of the aperiodic reporting mode, RIreporting may be effective only for CQI/PMI reporting in thecorresponding aperiodic reporting mode. CQI-PMI combinations capable ofbeing supported to all the rank values are shown in the following table8.

TABLE 8 PMI Feedback Type No PMI (OL, TD, single-antenna) with PMI (CL)PUSCH Wideband Mode 1-2: Multiple PMI CQI (Wideband CQI) RI Feedback1^(st) Wideband CQI (4 bit) Type 2^(nd) Wideband CQI (4 bit) if RI > 1subband PMIs on each subband UE Selected Mode 2-0 Mode 2-2: Multiple PMI(Subband CQI) RI (only for Open-Loop SM) RI Wideband CQI (4 bit) +Best-M CQI (2 bit) 1^(st) Wideband CQI (4 bit) + Best-M CQI(2 bit)Best-M index 2^(nd) Wideband CQI (4 bit) + Best-M CQI(2 bit) when RI >1, CQI of first codeword if RI > 1 Wideband PMI + Best-M PMI Best-Mindex Higher layer- Mode 3-0 Mode 3-1: Single PMI configured RI (onlyfor Open-Loop SM) RI (subband CQI) Wideband CQI (4 bit) + subband CQI (2bit) 1^(st) Wideband CQI (4 bit) + subband CQI when RI > 1, CQI of firstcodeword (2 bit) 2^(nd) Wideband CQI (4 bit) + subband CQI (2 bit) ifRI > 1 Wideband PMI

Mode 1-2 of Table 8 may indicate a WB feedback. In Mode 1-2, a preferredprecoding matrix for each subband may be selected from a codebook subseton the assumption of transmission only in the corresponding subband. TheUE may report one WB CQI at every codeword, and WB CQI may be calculatedon the assumption that data is transmitted on subbands of the entiresystem bandwidth (Set S) and the corresponding selected precoding matrixis used on each subband. The UE may report the selected PMI for eachsubband. In this case, the subband size may be given as shown in thefollowing table 9. In Table 9, if the system bandwidth is set to 6 or 7,this means no application of the subband size. That is, the systembandwidth of 6 or 7 means application of only WB CQI and no subbandstate.

TABLE 9 System Bandwidth Subband Size N_(RB) ^(DL) (k) 6-7 NA  8-10 411-26 4 27-63 6  64-110 8

In Table 8, Mode 3-0 and Mode 3-1 show a subband feedback configured bya higher layer (also called an upper layer).

In Mode 3-0, the UE may report a WB CQI value calculated on theassumption of data transmission on the set-S (total system bandwidth)subbands. The UE may also report one subband CQI value for each subband.The subband CQI value may be calculated on the assumption of datatransmission only at the corresponding subband. Even in the case ofRI>1, WB CQI and SB CQI may indicate a channel quality for Codeword 1.

In Mode 3-1, a single precoding matrix may be selected from a codebooksubset on the assumption of data transmission on the set-S subbands. TheUE may report one SB CQI value for each codeword on each subband. The SBCQI value may be calculated on the assumption of a single precodingmatrix used in all the subbands and data transmission on thecorresponding subband. The UE may report a WB CQI value for eachcodeword. The WB CQI value may be calculated on the assumption of asingle precoding matrix used in all the subbands and data transmissionon the set-S subbands. The UE may report one selected precoding matrixindicator. The SB CQI value for each codeword may be represented by adifferential WB CQI value using a 2-bit subband differential CQI offset.That is, the subbband differential CQI offset may be defined as adifferential value between a SB CQI index and a WB CQI index. Thesubband differential CQI offset value may be assigned to any one of fourvalues {−2, 0, +1, +2}. In addition, the subband size may be given asshown in the following table 7.

In Table 8, Mode 2-0 and Mode 2-2 illustrate a UE selected subbandfeedback. Mode 2-0 and Mode 2-2 illustrate reporting of the best-Maverages.

In Mode 2-0, the UE may select the set of M preferred subbands (i.e.,best-M) from among the entire system bandwidth (set S). The size of onesubband may be given as k, and k and M values for each set-S range maybe given as shown in the following table 10. In Table 10, if the systembandwidth is set to 6 or 7, this means no application of both thesubband size and the M value. That is, the system bandwidth of 6 or 7means application of only WB CQI and no subband state.

The UE may report one CQI value reflecting data transmission only at thebest-M subbands (i.e., M selected subbands). This CQI value may indicatea CQI for Codeword 1 even in the case of RI>1. In addition, the UE mayreport a WB CQI value calculated on the assumption of data transmissionon the set-S subbands. The WB CQI value may indicate a CQI for Codeword1 even in the case of RI>1.

TABLE 10 System Bandwidth Subband Size k N_(RB) ^(DL) (RBs) M 6-7 NA NA 8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

In Mode 2-2, the UE may select the set of M preferred subbands (i.e.,best-M) from among the set-S subbands (where the size of one subband isset to k). Simultaneously, one preferred precoding matrix may beselected from among a codebook subset to be used for data transmissionon the M selected subbands. The UE may report one CQI value for eachcodeword on the assumption that data transmission is achieved on Mselected subbands and one same selection precoding matrix is used ineach of the M subbands. The UE may report an indicator of one precodingmatrix selected for the M subbands. In addition, one precoding matrix(i.e., a precoding matrix different from the precoding matrix for theabove-mentioned M selected subbands) may be selected from among thecodebook subset on the assumption that data transmission is achieved onthe set-S subbands. The UE may report a WB CQI, that is calculated onthe assumption that data transmission is achieved on the set-S subbandsand one precoding matrix is used in all the subbands, at every codeword.The UE may report an indicator of the selected one precoding matrix inassociation with all the subbands.

In association with the entirety of UE-selected subband feedback modes(Mode 2-0 and Mode 2-2), the UE may report the positions of M selectedsubbands using a combination index (r), where r may be represented bythe following equation 16.

$\begin{matrix}{r = {\sum\limits_{i = 0}^{M - 1}\; {\langle\begin{matrix}{N - s_{i}} \\{M - i}\end{matrix}\rangle}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

In Equation 16, the set {s_(i)}_(i=0) ^(M−1), (1≦s_(i)≦N, s_(i)<s_(i+1))may include M sorted subband indexes. In Equation 14,

$\quad{\langle\begin{matrix}x \\y\end{matrix}\rangle}$

may indicate an extended binomial coefficient, which is set to

$\quad\begin{pmatrix}x \\y\end{pmatrix}$

in case of x≧y and is set to zero of 0 in case of x<y. Therefore, r mayhave a unique label and may be denoted by

$r \in {\left\{ {0,\ldots \mspace{14mu},{\begin{pmatrix}N \\M\end{pmatrix} - 1}} \right\}.}$

In addition, a CQI value for M selected subbands for each codeword maybe denoted by a relative differential value in association with a WBCQI. The relative differential value may be denoted by a differentialCQI offset level of 2 bits, and may have a value of ‘CQI index−WB CQIindex’ of M selected subbands. An available differential CQI value maybe assigned to any one of four values {+1, +2, +3, +4}.

In addition, the size(k) of supported subband and the M value may begiven as shown in Table 10. As shown in Table 10, k or M may be given asa function of a system bandwidth.

A label indicating the position of each of M selected subbands (i.e.,best-M subbands) may be denoted by L bits, where L is denoted by

$L = {\left\lceil {\log_{2}\begin{pmatrix}N \\M\end{pmatrix}} \right\rceil.}$

Precoder for 8 Tx Antennas

In the system (e.g., 3GPP LTE Release-10 system) for supporting theextended antenna structure, for example, MIMO transmission based on 8 Txantennas may be carried out, such that it is necessary to design thecodebook for supporting the MIMO transmission.

In order to report a CQI of a channel transmitted through 8 antennaports, the use of codebooks shown in Tables 11 to 18 may be considered.8 CSI antenna ports may be represented by indexes of antenna ports15˜22. Table 11 shows an example of the codebook for 1-layer CSI reportusing antenna ports 15 to 22. Table 12 shows an example of the codebookfor 2-layer CSI report using antenna ports 15 to 22. Table 13 shows anexample of the codebook for 3-layer CSI report using antenna ports 15 to22. Table 14 shows an example of the codebook for 4-layer CSI reportusing antenna ports 15 to 22. Table 15 shows an example of the codebookfor 5-layer CSI report using antenna ports 15 to 22. Table 16 shows anexample of the codebook for 6-layer CSI report using antenna ports 15 to22. Table 17 shows an example of the codebook for 7-layer CSI reportusing antenna ports 15 to 22. Table 18 shows an example of the codebookfor 8-layer CSI report using antenna ports 15 to 22.

In Tables 11 to 18, φ_(n) and v_(m) can be represented by the followingequation 17.

φ_(n) =e ^(jπn/2)

v _(m)=[1 e ^(j2πm/32) e ^(j4πm/32) e ^(j6πm/32)]^(T)  [Equation 17]

TABLE 11 i₂ i₁ 0 1 2 3 4 5 6 7 0-15 W_(2i) ₁ _(,0) ⁽¹⁾ W_(2i) ₁ _(,1)⁽¹⁾ W_(2i) ₁ _(,2) ⁽¹⁾ W_(2i) ₁ _(,3) ⁽¹⁾ W_(2i) ₁ _(+1,0) ⁽¹⁾ W_(2i) ₁_(+1,1) ⁽¹⁾ W_(2i) ₁ _(+1,2) ⁽¹⁾ W_(2i) ₁ _(+1,3) ⁽¹⁾ i₂ i₁ 8 9 10 11 1213 14 15 0-15 W_(2i) ₁ _(+2,0) ⁽¹⁾ W_(2i) ₁ _(+2,1) ⁽¹⁾ W_(2i) ₁ _(+2,2)⁽¹⁾ W_(2i) ₁ _(+2,3) ⁽¹⁾ W_(2i) ₁ _(+3,0) ⁽¹⁾ W_(2i) ₁ _(+3,1) ⁽¹⁾W_(2i) ₁ _(+3,2) ⁽¹⁾ W_(2i) ₁ _(+3,3) ⁽¹⁾${{where}\mspace{14mu} W_{m,n}^{(1)}} = {\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m} \\{\phi_{n}v_{m}}\end{bmatrix}}$

TABLE 12 i₂ i₁ 0 1 2 3 0-15 W_(2i) ₁ _(,2i) ₁ _(,0) ⁽²⁾ W_(2i) ₁ _(,2i)₁ _(,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,1)⁽²⁾ i₂ i₁ 4 5 6 7 0-15 W_(2i) ₁ _(+2,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+2,2i)₁ _(+2,1) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁_(+3,1) ⁽²⁾ i₂ i₁ 8 9 10 11 0-15 W_(2i) ₁ _(,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁_(,2i) ₁ _(+1,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁_(+2,1) ⁽²⁾ i₂ i₁ 12 13 14 15 0-15 W_(2i) ₁ _(,2i) ₁ _(+3,0) ⁽²⁾ W_(2i)₁ _(,2i) ₁ _(+3,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+1,2i)₁ _(+3,1) ⁽²⁾${{where}\mspace{14mu} W_{m,m^{\prime},n}^{(2)}} = {\frac{1}{4}\begin{bmatrix}v_{m} & v_{m^{\prime}} \\{\phi_{n}v_{m}} & {{- \phi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

TABLE 13 i₂ i₁ 0 1 2 3 0-3 W_(8i) ₁ _(,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ W_(8i) ₁_(+8,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(,8i) ₁ _(+8,8i) ₁₊₈ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+8,8i) ₁ _(,8i) ₁ ⁽³⁾ i₂ i₁ 4 5 6 7 0-3W_(8i) ₁ _(+2,8i) ₁ _(+2,4i) ₁ ₊₁₀ ⁽³⁾ W_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁₊₁₀ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+2,8i) ₁ _(+10,8i) ₁ ₊₁₀ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁ ₊₂ ⁽³⁾ i₂ i₁ 8 9 10 11 0-3W_(8i) ₁ _(+4,8i) ₁ _(+4,8i) ₁ ₊₁₂ ⁽³⁾ W_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁₊₁₂ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+4,8i) ₁ _(+12,8i) ₁ ₊₁₂ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁ ₊₄ ⁽³⁾ i₂ i₁ 12 13 14 15 0-3W_(8i) ₁ _(+6,8i) ₁ _(+6,8i) ₁ ₊₁₄ ⁽³⁾ W_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁₊₁₄ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+6,8i) ₁ _(+14,8i) ₁ ₊₁₄ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁ ₊₆ ⁽³⁾${{{where}\mspace{14mu} W_{m,m^{\prime},m^{''}}^{(3)}} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & {- v_{m^{\prime}}} & {- v_{m^{''}}}\end{bmatrix}}},{{\overset{\sim}{W}}_{m,m^{\prime},m^{''}}^{(3)} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & v_{m^{\prime}} & {- v_{m^{''}}}\end{bmatrix}}}$

TABLE 14 i₂ i₁ 0 1 2 3 0-3 W_(8i) ₁ _(,8i) ₁ _(+8,0) ⁽⁴⁾ W_(8i) ₁ _(,8i)₁ _(+8,1) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁ _(+10,0) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁_(+10,1) ⁽⁴⁾ i₂ i₁ 4 5 6 7 0-3 W_(8i) ₁ _(+4,8i) ₁ _(+12,0) ⁽⁴⁾ W_(8i) ₁_(+4,8i) ₁ _(+12,1) ⁽⁴⁾ W_(8i) ₁ _(+6,8i) ₁ _(+14,0) ⁽⁴⁾ W_(8i) ₁_(+6,8i) ₁ _(+14,1) ⁽⁴⁾${{where}\mspace{14mu} W_{m,m^{\prime},n}^{(4)}} = {\frac{1}{\sqrt{32}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m} & v_{m^{\prime}} \\{\phi_{n}v_{m}} & {\phi_{n}v_{m^{\prime}}} & {{- \phi_{n}}v_{m}} & {{- \phi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

TABLE 15 i₂ i₁ 0 0-3$W_{i_{1}}^{(5)} = {\frac{1}{\sqrt{40}}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16}\end{bmatrix}}$

TABLE 16 i₂ i₁ 0 0-3$W_{i_{1}}^{(6)} = {\frac{1}{\sqrt{48}}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 16} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16} & {- v_{{2i_{1}} + 16}}\end{bmatrix}}$

TABLE 17 i₂ i₁ 0 0-3$W_{i_{1}}^{(7)} = {\frac{1}{\sqrt{56}}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 24} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16} & {- v_{{2i_{1}} + 16}} & v_{{2i_{1}} + 24}\end{bmatrix}}$

TABLE 18 i₂ i₁ 0 0 $W_{i_{1}}^{(8)} = {\frac{1}{8}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 24} & v_{{2i_{1}} + 24} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16} & {- v_{{2i_{1}} + 16}} & v_{{2i_{1}} + 24} & {- v_{{2i_{1}} + 24}}\end{bmatrix}}$

Embodiment 1

A first embodiment (Embodiment 1) discloses a method for deciding thenumber of bits of different precoder indexes constructing the entireprecoder.

Tables 11 to 18 show codebooks for enabling a BS (or eNB) having 8 Txantennas in the 3GPP LTE system to report a CSI. The CSI reportcodebooks shown in Tables 11 to 18 may decide the codebook elementaccording to two kinds of feedback reports. Although Tables 11 to 18represent two feedback report values as i1 and i2, i1 and i2 correspondto one precoder index W1 (or PMI1) and another precoder index W2 (orPMI2), respectively. Two report values may have different timing points,and may be established to have different frequency granularities. Fordata transmission, the number (# of element) of constituent elements ofthe codebook may have different values according to the number ofUE-recommended ranks, as represented by the following Table 19.

TABLE 19 Rank 1 2 3 4 5 6 7 8 # of element for i1 16 16 4 4 4 4 4 1 # ofelement for i2 16 16 16 8 1 1 1 1

In Table 19, i1 may be defined to have an element of 16, 4 or accordingto the rank, and i2 may be defined to have an element of 16, 8 oraccording to the rank. For feedback, i1 may be represented by 0 to 4bits, and i2 may be represented by 0 to 4 bits. A maximum number of bitscapable of expressing i1 and i2 according to the rank can be representedby the following Table 20.

TABLE 20 Rank 1 2 3 4 5 6 7 8 Maximum bits for i1 4 4 2 2 2 2 2 0Maximum bits for i2 4 4 4 3 0 0 0 0

Due to limitation of control channel capacity defined to report feedbackinformation, bits capable of representing i1 and i2 for CSI report maybe restricted. That is, the i1 and i2 values must be transmitted toreport a CSI. If an indicator for the i1 value and/or an indicator forthe i2 value may be transmitted along with RI or CQI, an error ratesimilar to that of a channel that reports RI or CQI defined in thelegacy 3GPP LTE Release-8 or Release-9 may be implemented and at thesame time feedback information may be transmitted as necessary.

In the case where the indicator for the i1 value and/or the indicatorfor the i2 value are simultaneously transmitted along with RI or CQI,for example, RI may be reported through one subframe, and an indicatorfor the i1 value, an indicator for the i2 value and a CQI may besimultaneously reported through another subframe. In another example, RIand the indicator for i1 may be simultaneously reported through onesubframe, and the indicator for i2 and a CQI may be simultaneouslytransmitted through another subframe.

The legacy 3GPP LTE Release-8 or Release-9 assumes transmission of amaximum of 2 bits for the RI. In case of RI transmission through aPUCCH, the same coding method as in ACK/NACK transmission may be used.In addition, it is assumed that a maximum of 11 bits is transmitted toreport CQI/PMI, such that the coding may be carried out using aReed-Muller (RM) code that is capable of supporting a maximum of 13bits.

If it is assumed that the system (e.g., 3GPP LTE Release-10 system)supporting the extended antenna structure simultaneously reports i1, i2,and CQI (i1/i2/CQI), a maximum of 15 (=4+4+7) bits may be requisite forRank-1 or Rank-2. To transmit 15 bits, the coding method for extendingthe legacy RM code may be used, or a control signal may be reportedusing the conventional convolution code. In addition, in order toimplement the same level as that of maximum bits defined in the legacysystem, a method for reducing the size of indicator bits for i1 and i2may be used as necessary.

Table 21 shows numbers of bits needed to simultaneously report i1, i2and CQI (i1/i2/CQI). If the indicator bits for i1 and i2 are set to 0∫4,the number of bits transmitted in one subframe is shown in Table 21. Inaddition, according to the rank, the number of indicator bits for i1 ori2 may be a fullset or subset. For example, if the i1 indicator bit isset to 4 and the i2 indicator bit is set to 4, all the fullsets of acodebook may be used to transmit Rank-1 and Rank-2. Alternatively, inthe case where 2 bits are used for i1 or (W1) and 4 bits are used for i2(or W2), the subset of i1 may be used in Rank-1 or Rank-2, the fullsetof i2 may be used, and all fullsets of i1 and i2 may be used in Rank-3.In Table 21, F may represent the fullset, and S may represent thesubset. In addition, in association with each expression (F/F, F/S, S/For S/S) of Table 21, a number located in front of a specific symbol (/)represents bits for i1 and another number located behind the symbol (/)represents bits for i2.

TABLE 21 Rank R i1 i2 i1 + i2 + CQI 1 2 3 4 5 6 7 8 1/2/3 4 4 4 + 4 + 7F/F F/F — — — — — — 3 4 + 3 + 7 F/S F/S — — — — — — 2 4 + 2 + 7 F/S F/S— — — — — — 1 4 + 1 + 7 F/S F/S — — — — — — 0 4 + 0 + 7 F/S F/S — — — —— — 3 4 3 + 4 + 7 S/F S/F — — — — — — 3 3 + 3 + 7 S/S S/S — — — — — — 23 + 2 + 7 S/S S/S — — — — — — 1 3 + 1 + 7 S/S S/S — — — — — — 0 3 + 0 +7 S/S S/S — — — — — — 2 4 2 + 4 + 7 S/F S/F F/F — — — — — 3 2 + 3 + 7S/S S/S F/S F/F — — — — 2 2 + 2 + 7 S/S S/S F/S F/S — — — — 1 2 + 1 + 7S/S S/S F/S F/S — — — — 0 2 + 0 + 7 S/S S/S F/S F/S F/F F/F F/F — 1 41 + 4 + 7 S/F S/F S/F — — — — — 3 1 + 3 + 7 S/S S/S S/F S/F — — — — 21 + 2 + 7 S/S S/S S/S S/S — — — — 1 1 + 1 + 7 S/S S/S S/S S/S — — — — 01 + 0 + 7 S/S S/S S/S S/S S/F S/F S/F — 0 0 0 + 0 + 7 S/S S/S S/S S/SS/S S/S S/S F/F

To apply the legacy coding method to PUCCH feedback transmission or toobtain an error rate similar to that of the conventional feedbackchannel, 13 bits or less may be transmitted within one subframe. In thiscase, when using the subset including only too small number of codebookelements, the probability that the codebook element for expressing a CSIappropriate for an actual channel state is contained in thecorresponding subset is gradually decreased, resulting in a reduction intransmission throughput. Therefore, the number of feedback bits must bereduced and the subset of an appropriate level must be used.

For example, for Rank-1 and Rank-2, a maximum of 4 bits may be requestedfor each of i1 and i2. The subset of index in which ‘(bits for the i1indicator/bits for the i2 indicator)’ is set to any of (4/3), (4/2),(3/3), (3/2), (2/3), (2/2), etc. may be used as necessary.

In addition, the fullset or subset of index may be used according to therank. For example, in order to implement the level corresponding to amaximum of 11 bits, ‘2 bits/2 bits’ may be used for i1 and i2 (i1/i2).In this case, ‘2 bits/2 bits’ may be used at Ranks 1 to 4, ‘2 bits/0bit’ may be used at Ranks 5 to 7, and ‘0 bit/0 bit’ may be used atRank-8. Alternatively, in order to implement the level corresponding toa maximum of 13 bits, ‘3 bits/2 bits’ may be used for i1 and i2 (i1/i2).In this case, ‘3 bits/2 bits’ may be used at Ranks 1 and 2, ‘2 bits/4bits’ may be used at Rank-3, ‘2 bits/3 bits’ may be used at Rank-4, ‘2bits/0 bit’ may be used at Ranks 5 to 7, and ‘0 bit/0 bit’ may be usedat Rank-8. Table 22 shows exemplary bit numbers capable of being usedfor i1 and i2 (i1/i2) for each rank.

TABLE 22 Rank (i1/i2) 1 (4/2), (3/3), (3/2), (2/3), (2/2) 2 (4/2),(3/3), (3/2), (2/3), (2/2) 3 (2/4), (2/3), (2/2), (2/1), (2/0), (1/4),(1/3), (1/2), (1/1), (1/0) 4 (2/3), (2/2), (2/1), (2/0), (1/3), (1/2),(1/1) 5 (2/0) 6 (2/0) 7 (2/0) 8 (0/0)

Table 23 shows bits required either when the RI and the i1 index aresimultaneously transmitted within one subframe or when the i2 index andthe CQI are simultaneously transmitted within another subframe.

TABLE 23 Rank RI i1 i2 RI + i1 i2 + CQI 1 2 3 4 5 6 7 8 3 4 4 3 + 4 4 +7 F/F F/F — — — — — — 3 3 + 7 F/S F/S — — — — — — 2 2 + 7 F/S F/S — — —— — — 1 1 + 7 F/S F/S — — — — — — 0 0 + 7 F/S F/S — — — — — — 3 4 3 + 34 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 2 2 + 7 S/S S/S —— — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S — — — — — — 2 43 + 2 4 + 7 S/F S/F F/F — — — — — 3 3 + 7 S/S S/S F/S F/F — — — — 2 2 +7 S/S S/S F/S F/S — — — — 1 1 + 7 S/S S/S F/S F/S — — — — 0 0 + 7 S/SS/S F/S F/S F/F F/F F/F — 1 4 3 + 1 4 + 7 S/F S/F S/F — — — — — 3 3 + 7S/S S/S S/F S/F — — — — 2 2 + 7 S/S S/S S/S S/S — — — — 1 1 + 7 S/S S/SS/S S/S — — — — 0 0 + 7 S/S S/S S/S S/S S/F S/F S/F — 0 0 3 + 0 0 + 7S/S S/S S/S S/S S/S S/S S/S F/F 2 4 4 2 + 4 4 + 7 F/F F/F — — — — — — 33 + 7 F/S F/S — — — — — — 2 2 + 7 F/S F/S — — — — — — 1 1 + 7 F/S F/S —— — — — — 0 0 + 7 F/S F/S — — — — — — 3 4 2 + 3 4 + 7 S/F S/F — — — — —— 3 3 + 7 S/S S/S — — — — — — 2 2 + 7 S/S S/S — — — — — — 1 1 + 7 S/SS/S — — — — — — 0 0 + 7 S/S S/S — — — — — — 2 4 2 + 2 4 + 7 S/F S/F F/F— — — — — 3 3 + 7 S/S S/S F/S F/F — — — — 2 2 + 7 S/S S/S F/S F/S — — —— 1 1 + 7 S/S S/S F/S F/S — — — — 0 0 + 7 S/S S/S F/S F/S — — — — 1 42 + 1 4 + 7 S/F S/F S/F — — — — — 3 3 + 7 S/S S/S S/F S/F — — — — 2 2 +7 S/S S/S S/S S/S — — — — 1 1 + 7 S/S S/S S/S S/S — — — — 0 0 + 7 S/SS/S S/S S/S — — — — 0 0 2 + 0 0 + 7 S/S S/S S/S S/S — — — — 1 4 4 1 + 44 + 7 F/F F/F — — — — — — 3 3 + 7 F/S F/S — — — — — — 2 2 + 7 F/S F/S —— — — — — 1 1 + 7 F/S F/S — — — — — — 0 0 + 7 F/S F/S — — — — — — 3 41 + 3 4 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 2 2 + 7 S/SS/S — — — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S — — — — — —2 4 1 + 2 4 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 2 2 + 7S/S S/S — — — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S — — — —— — 1 4 1 + 1 4 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 22 + 7 S/S S/S — — — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S —— — — — — 0 0 1 + 0 0 + 7 S/S S/S — — — — — —

If the maximum number of Ranks reported by a UE is determined accordingto either a maximum rank capable of being received at the UE or amaximum rank to be transmitted from an eNB, a bit for Rank indicationmay be determined. Provided that RI and i1 are combined andsimultaneously transmitted, a maximum number of bits requisite forfeedback may be 7 (=3+4) bits, and a minimum number of bits may be 5(=1+4) bits.

Rank information is basically used to select/calculate other feedbackinformation, such that it is necessary to robustly transmit the rankinformation. Thus, it is preferable that the number of bits contained ina subframe corresponding to rank transmission be reduced as much aspossible. For such transmission, a method for reducing the number ofbits of the i1 indicator may be used as necessary. Considering theabove-mentioned condition, Table 24 exemplarily shows bit numberscapable of being used for i1 and i2 (i1/i2) for each rank.

TABLE 24 Rank (i1/i2) 1 (3/4), (3/3), (3/2), (2/4), (2/3), (2/2) 2(3/4), (3/3), (3/2), (2/4), (2/3), (2/2) 3 (2/4), (2/3), (2/2), (2/1),(2/0), (1/4), (1/3), (1/2), (1/1), (1/0) 4 (2/3), (2/2), (2/1), (2/0),(1/3), (1/2), (1/1) 5 (2/0), (1/0) 6 (2/0), (1/0) 7 (2/0), (1/0) 8 (0/0)

In case of setting the subset of the i1/i2 indicators, for example, thei1 and i2 subsets may be designed to have different sizes according to apreferred rank. In another example, the i1 and i2 subsets may bedesigned to have different sizes according to UE category. The UEcategory may be classified according to UE capability.

Embodiment 2

A method for setting the codebook subset through different precoderindexes (i1/i2) according to the present invention will hereinafter bedescribed in detail.

Table 25 shows another example of a codebook appropriate for Rank-1 CSIreport shown in Table 11. Rank-1 codeword may be configured on the basisof 4 Tx DFT vector (v_(m)), and may be represented by a combination ofthe 4Tx DFT vector (v_(m)) and a phase (φ_(n)). If the i1 index isdefined as 0 to 15 and the i2 index is defined as 0 to 15, the codebookmay be configured by both v_(m) having a 32PSK (Phase Shift Keying)phase and φ_(n) having a QPSK (Quadrature PSK) phase. In this case, thesame element may be repeated between contiguous indexes of the i1 value.

TABLE 25 i2 i1 0 1 2 3 4 5 6 7 0 V0 V0 V0 V0 V1 V1 V1 V1 V0 jV0 −V0 −jV0V1 jV1 −V1 −jV1 1 V2 V2 V2 V2 V3 V3 V3 V3 V2 jV2 −V2 −jV2 V3 jV3 −V3−jV3 2 V4 V4 V4 V4 V5 V5 V5 V5 V4 jV4 −V4 −jV4 V5 jV5 −V5 −jV5 3 V6 V6V6 V6 V7 V7 V7 V7 V6 jV6 −V6 −jV6 V7 jV7 −V7 −jV7 4 V8 V8 V8 V8 V9 V9 V9V9 V8 jV8 −V8 −jV8 V9 jV9 −V9 −jV9 5 V10 V10 V10 V10 V11 V11 V11 V11 V10jV10 −V10 −jV10 V11 jV11 −V11 −jV11 6 V12 V12 V12 V12 V13 V13 V13 V13V12 jV12 −V12 −jV12 V13 jV13 −V13 −jV13 7 V14 V14 V14 V14 V15 V15 V15V15 V14 jV14 −V14 −jV14 V15 jV15 −V15 −jV15 8 V16 V16 V16 V16 V17 V17V17 V17 V16 jV16 −V16 −jV16 V17 jV17 −V17 −jV17 9 V18 V18 V18 V18 V19V19 V19 V19 V18 jV18 −V18 −jV18 V19 jV19 −V19 −jV19 10 V20 V20 V20 V20V21 V21 V21 V21 V20 jV20 −V20 −jV20 V21 jV21 −V21 −jV21 11 V22 V22 V22V22 V23 V23 V23 V23 V22 jV22 −V22 −jV22 V23 jV23 −V23 −jV23 12 V24 V24V24 V24 V25 V25 V25 V25 V24 jV24 −V24 −jV24 V25 jV25 −V25 −jV25 13 V26V26 V26 V26 V27 V27 V27 V27 V26 jV26 −V26 −jV26 V27 jV27 −V27 −jV27 14V28 V28 V28 V28 V29 V29 V29 V29 V28 jV28 −V28 −jV28 V29 jV29 −V29 −jV2915 V30 V30 V30 V30 V31 V31 V31 V31 V30 jV30 −V30 −jV30 V31 jV31 −V31−jV31 i2 i1 8 9 10 11 12 13 14 15 0 V2 V2 V2 V2 V3 V3 V3 V3 V2 jV2 −V2−jV2 V3 jV3 −V3 −jV3 1 V4 V4 V4 V4 V5 V5 V5 V5 V4 jV4 −V4 −jV4 V5 jV5−V5 −jV5 2 V6 V6 V6 V6 V7 V7 V7 V7 V6 jV6 −V6 −jV6 V7 jV7 −V7 −jV7 3 V8V8 V8 V8 V9 V9 V9 V9 V8 jV8 −V8 −jV8 V9 jV9 −V9 −jV9 4 V10 V10 V10 V10V11 V11 V11 V11 V10 jV10 −V10 −jV10 V11 jV11 −V11 −jV11 5 V12 V12 V12V12 V13 V13 V13 V13 V12 jV12 −V12 −jV12 V13 jV13 −V13 −jV13 6 V14 V14V14 V14 V15 V15 V15 V15 V14 jV14 −V14 −jV14 V15 jV15 −V15 −jV15 7 V16V16 V16 V16 V17 V17 V17 V17 V16 jV16 −V16 −jV16 V17 jV17 −V17 −jV17 8V18 V18 V18 V18 V19 V19 V19 V19 V18 jV18 −V18 −jV18 V19 jV19 −V19 −jV199 V20 V20 V20 V20 V21 V21 V21 V21 V20 jV20 −V20 −jV20 V21 jV21 −V21−jV21 10 V22 V22 V22 V22 V23 V23 V23 V23 V22 jV22 −V22 −jV22 V23 jV23−V23 −jV23 11 V24 V24 V24 V24 V25 V25 V25 V25 V24 jV24 −V24 −jV24 V25jV25 −V25 −jV25 12 V26 V26 V26 V26 V27 V27 V27 V27 V26 jV26 −V26 −jV26V27 jV27 −V27 −jV27 13 V28 V28 V28 V28 V29 V29 V29 V29 V28 jV28 −V28−jV28 V29 jV29 −V29 −jV29 14 V30 V30 V30 V30 V31 V31 V31 V31 V30 jV30−V30 −jV30 V31 jV31 −V31 −jV31 15 V0 V0 V0 V0 V1 V1 V1 V1 V0 jV0 −V0−jV0 V1 jV1 −V1 −jV1

Accordingly, in order to configure the subset of a codebook, a methodfor limiting a phase of a DFT matrix constructing the vector of v_(m) orthe phase of φ_(n), and a method for constructing the i1 value usingdifferent codebook elements at different i1 indexes of codebook elementscontained in one i1 value may be considered. In this way, the codebooksubset may be constructed.

According to whether the i1 or i2 subset is used, DFT vector of v_(m)and a phase of φ_(n) may be determined. For example, it is assumed that,in order to indicate the i1 value, 3 bits may be used and 8 even indexes(0, 2, 4, 6, 8, 10, 12, 14) may be used. It is also assumed that, inorder to indicate the i1 value, 3 bits may be used and 8 indexes (0, 1,2, 3, 8, 9, 10, 11) may be used. Under these assumption, a 4Tx DFTvector having a 16PSK phase for the v_(m) value and a QPSK for the phase(φ_(n))) may be configured.

As described above, when deciding the indication bit for the i1 valueand the indication bit for the i2 value, one phase of the 4Tx DFT vectorfor constructing the v_(m) value and the other phase for constructingthe phase (φ_(n)) according to a combination of indexes appropriate forindividual bits may be represented by the following table 26.

TABLE 26 Bit for i1 Bit for i2 (elements (elements number) number) ν_(m)φ_(n) 1 2 (4n, n: 0~3) 1 (0, 1) QPSK {1, j} 2 2 (4n, n: 0~3) 1 (0, 2)QPSK BPSK 3 2 (4n, n: 0~3) 2 (0~3) QPSK QPSK 4 2 (4n, n: 0~3) 2 (2m, m:0~3) QPSK + QPSK(2pi/32) BPSK 5 2 (4n, n: 0~3) 3 (0~7) QPSK +QPSK(2pi/32) QPSK 6 2 (4n, n: 0~3) 3 (0~3, 8~11) QPSK + QPSK(2 × QPSK2pi/32) 7 2 (4n, n: 0~3) 3 (2m, m: 0~7) QPSK + QPSK(2pi/32) + BPSKQPSK(2 × 2pi/32) + QPSK(2 × 3pi/32) 8 2 (4n, n: 0~3) 4 (0~15) QPSK +QPSK(2pi/32) + QPSK QPSK(2 × 2pi/32) + QPSK(2 × 3pi/32) 9 3 (2n, n: 0~7)1 (0, 1)  8 PSK {1, j} 10 3 (2n, n: 0~7) 1 (0, 2)  8 PSK BPSK 11 3 (2n,n: 0~7) 2 (0~3)  8 PSK QPSK 12 3 (2n, n: 0~7) 2 (2m, m: 0~3)  8 PSK + 8BPSK PSK(2pi/32) 13 3 (2n, n: 0~7) 3 (0~7)  8 PSK + 8 QPSK PSK(2pi/32)14 3 (2n, n: 0~7) 3 (0~3, 8~11) 16 PSK QPSK 15 3 (2n, n: 0~7) 3 (2m, m:0~7) 32 PSK BPSK 16 3 (2n, n: 0~7) 4 (0~15) 32 PSK QPSK 17 4 (0~15) 1(0, 1) 16 PSK {1, j} 18 4 (0~15) 1 (0, 2) 16 PSK BPSK 19 4 (0~15) 2(0~3) 16 PSK QPSK 20 4 (0~15) 2 (2m, m: 0~3) 32 PSK BPSK 21 4 (0~15) 3(0~7) 32 PSK QPSK 22 4 (0~15) 3 (0~3, 8~11) 16 PSK (Overraped) QPSK 23 4(0~15) 3 (2m, m: 0~7) 32 PSK (Overraped) BPSK 24 4 (0~15) 4 (0~15) 32PSK (Overraped) QPSK

Table 27 shows another example of a codebook appropriate for Rank-2 CSIreport shown in Table 12. In the Rank-2 CSI report, 16 indexes (0 to 15)are defined for each of the i1 and i2 values.

TABLE 27 i2 0 1 2 3 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st)2^(nd) i1 0 2 1 3 4 6 5 7 0 V0 V0 V0 V0 V1 V1 V1 V1 V0 −V0 jV0 −jV0 V1−V1 jV1 −jV1 1 V2 V2 V2 V2 V3 V3 V3 V3 V2 −V2 jV2 −jV2 V3 −V3 jV3 −jV3 2V4 V4 V4 V4 V5 V5 V5 V5 V4 −V4 jV4 −j V4 V5 −V5 iV5 −j V5 3 V6 V6 V6 V6V7 V7 V7 V7 V6 −V6 jV6 −j V6 V7 −V7 jV7 −j V7 4 V8 V8 V8 V8 V9 V9 V9 V9V8 −V8 jV8 −j V8 V9 −V9 jV9 −j V9 5 V10 V10 V10 V10 V11 V11 V11 V11 V10−V10 jV10 −j V10 V11 −V11 jV11 −j V11 6 V12 V12 V12 V12 V13 V13 V13 V13V12 −V12 jV12 −j V12 V13 −V13 jV13 −j V13 7 V14 V14 V14 V14 V15 V15 V15V15 V14 −V14 jV14 −j V14 V15 −V15 jV15 −j V15 8 V16 V16 V16 V16 V17 V17V17 V17 V16 −V16 jV16 −j V16 V17 −V17 jV17 −j V17 9 V18 V18 V18 V18 V19V19 V19 V19 V18 −V18 jV18 −j V18 V19 −V19 jV19 −j V19 10 V20 V20 V20 V20V21 V21 V21 V21 V20 −V20 jV20 −j V20 V21 −V21 jV21 −j V21 11 V22 V22 V22V22 V23 V23 V23 V23 V22 −V22 jV22 −j V22 V23 −V23 jV23 −j V23 12 V24 V24V24 V24 V25 V25 V25 V25 V24 −V24 jV24 −j V24 V25 −V25 jV25 −j V25 13 V26V26 V26 V26 V27 V27 V27 V27 V26 −V26 jV26 −j V26 V27 −V27 jV27 −j V27 14V28 V28 V28 V28 V29 V29 V29 V29 V28 −V28 jV28 −j V28 V29 −V29 jV29 −jV29 15 V30 V30 V30 V30 V31 V31 V31 V31 V30 −V30 jV30 −j V30 V31 −V31jV31 −j V31 i2 4 5 6 7 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st)2^(nd) i1 8 10 9 11 12 14 13 15 0 V2 V2 V2 V2 V3 V3 V3 V3 V2 −V2 jV2−jV2 V3 −V3 jV3 −jV3 1 V4 V4 V4 V4 V5 V5 V5 V5 V4 −V4 jV4 −j V4 V5 −V5jV5 −j V5 2 V6 V6 V6 V6 V7 V7 V7 V7 V6 −V6 jV6 −j V6 V7 −V7 jV7 −j V7 3V8 V8 V8 V8 V9 V9 V9 V9 V8 −V8 jV8 −j V8 V9 −V9 jV9 −j V9 4 V10 V10 V10V10 V11 V11 V11 V11 V10 −V10 jV10 −j V10 V11 −V11 jV11 −j V11 5 V12 V12V12 V12 V13 V13 V13 V13 V12 −V12 jV12 −j V12 V13 −V13 jV13 −j V13 6 V14V14 V14 V14 V15 V15 V15 V15 V14 −V14 jV14 −j V14 V15 −V15 jV15 −j V15 7V16 V16 V16 V16 V17 V17 V17 V17 V16 −V16 jV16 −j V16 V17 −V17 jV17 −jV17 8 V18 V18 V18 V18 V19 V19 V19 V19 V18 −V18 jV18 −j V18 V19 −V19 jV19−j V19 9 V20 V20 V20 V20 V21 V21 V21 V21 V20 −V20 jV20 −j V20 V21 −V21jV21 −j V21 10 V22 V22 V22 V22 V23 V23 V23 V23 V22 −V22 jV22 −j V22 V23−V23 jV23 −j V23 11 V24 V24 V24 V24 V25 V25 V25 V25 V24 −V24 jV24 −j V24V25 −V25 jV25 −j V25 12 V26 V26 V26 V26 V27 V27 V27 V27 V26 −V26 jV26 −jV26 V27 −V27 jV27 −j V27 13 V28 V28 V28 V28 V29 V29 V29 V29 V28 −V28jV28 −j V28 V29 −V29 jV29 −j V29 14 V30 V30 V30 V30 V31 V31 V31 V31 V30−V30 jV30 −j V30 V31 −V31 jV31 −j V31 15 V0 V0 V0 V0 V1 V1 V1 V1 V0 −V0jV0 −jV0 V1 −V1 jV1 −jV1 i2 8 9 10 11 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st)2^(nd) 1^(st) 2^(nd) i1 0 6 1 7 4 10 5 9 0 V0 V1 V0 V1 V1 V2 V1 V2 V0−V1 jV0 −jV1 V1 −V2 jV1 −jV2 1 V2 V3 V2 V3 V3 V4 V3 V4 V2 −V3 jV2 −jV3V3 −V4 jV3 −j V4 2 V4 V5 V4 V5 V5 V6 V5 V6 V4 −V5 jV4 −j V5 V5 −V6 jV5−j V6 3 V6 V7 V6 V7 V7 V8 V7 V8 V6 −V7 jV6 −j V7 V7 −V8 jV7 −j V8 4 V8V9 V8 V9 V9 V10 V9 V10 V8 −V9 jV8 −j V9 V9 −V10 jV9 −j V10 5 V10 V11 V10V11 V11 V12 V11 V12 V10 −V11 jV10 −j V11 V11 −V12 jV11 −j V12 6 V12 V13V12 V13 V13 V14 V13 V14 V12 −V13 jV12 −j V13 V13 −V14 jV13 −j V14 7 V14V15 V14 V15 V15 V16 V15 V16 V14 −V15 jV14 −j V15 V15 −V16 jV15 −j V16 8V16 V17 V16 V17 V17 V18 V17 V18 V16 −V17 jV16 −j V17 V17 −V18 jV17 −jV18 9 V18 V19 V18 V19 V19 V20 V19 V20 V18 −V19 jV18 −j V19 V19 −V20 jV19−j V20 10 V20 V21 V20 V21 V21 V22 V21 V22 V20 −V21 jV20 −j V21 V21 −V22jV21 −j V22 11 V22 V23 V22 V23 V23 V24 V23 V24 V22 −V23 jV22 −j V23 V23−V24 jV23 −j V24 12 V24 V25 V24 V25 V25 V26 V25 V26 V24 −V25 jV24 −j V25V25 −V26 jV25 −j V26 13 V26 V27 V26 V27 V27 V28 V27 V28 V26 −V27 jV26 −jV27 V27 −V28 jV27 −j V28 14 V28 V29 V28 V29 V29 V30 V29 V30 V28 −V29jV28 −j V29 V29 −V30 jV29 −j V30 15 V30 V31 V30 V31 V31 V0 V31 V0 V30−V31 jV30 −j V31 V31 −V0 jV31 −jV0 i2 12 13 14 15 1^(st) 2^(nd) 1^(st)2^(nd) 1^(st) 2^(nd) 1^(st) 2^(nd) i1 0 14 1 13 4 14 5 15 0 V0 V3 V0 V3V1 V3 V1 V3 V0 −V3 jV0 −jV3 V1 −V3 jV1 −jV3 1 V2 V5 V2 V5 V3 V5 V3 V5 V2−V5 jV2 −j V5 V3 −V5 jV3 −j V5 2 V4 V7 V4 V7 V5 V7 V5 V7 V4 −V7 jV4 −jV7 V5 −V7 jV5 −j V7 3 V6 V9 V6 V9 V7 V9 V7 V9 V6 −V9 jV6 −j V9 V7 −V9jV7 −j V9 4 V8 V11 V8 V11 V9 V11 V9 V11 V8 −V11 jV8 −j V11 V9 −V11 jV9−j V11 5 V10 V13 V10 V13 V11 V13 V11 V13 V10 −V13 jV10 −j V13 V11 −V13jV11 −j V13 6 V12 V15 V12 V15 V13 V15 V13 V15 V12 −V15 jV12 −j V15 V13−V15 jV13 −j V15 7 V14 V17 V14 V17 V15 V17 V15 V17 V14 −V17 jV14 −j V17V15 −V17 jV15 −j V17 8 V16 V19 V16 V19 V17 V19 V17 V19 V16 −V19 jV16 −jV19 V17 −V19 jV17 −j V19 9 V18 V21 V18 V21 V19 V21 V19 V21 V18 −V21 jV18−j V21 V19 −V21 jV19 −j V21 10 V20 V23 V20 V23 V21 V23 V21 V23 V20 −V23jV20 −j V23 V21 −V23 jV21 −j V23 11 V22 V25 V22 V25 V23 V25 V23 V25 V22−V25 jV22 −j V25 V23 −V25 jV23 −j V25 12 V24 V27 V24 V27 V25 V27 V25 V27V24 −V27 jV24 −j V27 V25 −V27 jV25 −j V27 13 V26 V29 V26 V29 V27 V29 V27V29 V26 −V29 jV26 −j V29 V27 −V29 jV27 −j V29 14 V28 V31 V28 V31 V29 V31V29 V31 V28 −V31 jV28 −j V31 V29 −V31 jV29 −j V31 15 V30 V1 V30 V1 V31V1 V31 V1 V30 −V1 jV30 −jV1 V31 −V1 jV31 −jV1

When the indication bit for the i1 value and the indication bit for thei2 value are decided in the codebook subset configuration, a phase ofthe 4Tx DFT vector constructing the v_(m) value and a phase of φ_(n)according to a combination of indexes appropriate for each bit may berepresented by Table 26.

The DFT vector of v_(m) and the phase of φ_(n) are determined accordingto whether the i1 or i2 subset is used. As shown in Table 27, whendeciding the indication bit for the i1 value and the indication bit forthe i2 value, one phase of the 4Tx DFT vector for constructing the v_(m)value and the other phase for constructing the phase (φ_(n))) accordingto a combination of indexes appropriate for each bit may be representedby the following table 28.

TABLE 28 Bit for i1 Bit for i2 (elements number) (elements number) ν_(m)φ_(n) 1 2 (4n, n: 0~3) 1 (0, 1) QPSK + QPSK(2pi/32) QPSK 2 2 (4n, n:0~3) 1 (0, 2) QPSK + QPSK(2pi/32) BPSK 3 2 (4n, n: 0~3) 2 (0~3) QPSK +QPSK(2pi/32) QPSK 4 2 (4n, n: 0~3) 2 (0, 1, 4, 5) QPSK + QPSK(2 ×2pi/32) QPSK 5 2 (4n, n: 0~3) 2 (2m, m: 0~3) QPSK + QPSK(2pi/32) + BPSKQPSK(2 × 2pi/32) + QPSK(2 × 3pi/32) 6 2 (4n, n: 0~3) 2 (2m + 8, m: 0~3)QPSK + QPSK(2pi/32) + BPSK QPSK(2 × 2pi/32) + QPSK(2 × 3pi/32) 7 2 (4n,n: 0~3) 3 (0~7) QPSK + QPSK(2pi/32) + QPSK QPSK(2 × 2pi/32) + QPSK(2 ×3pi/32) 8 2 (4n, n: 0~3) 3 (8~15) QPSK + QPSK(2pi/32) + QPSK QPSK(2 ×2pi/32) + QPSK(2 × 3pi/32) 9 2 (4n, n: 0~3) 3 (2m, m: 0~7) QPSK +QPSK(2pi/32) + BPSK QPSK(2 × 2pi/32) + QPSK(2 × 3pi/32) 10 2 (4n, n:0~3) 4 (0~15) QPSK + QPSK(2pi/32) + QPSK QPSK(2 × 2pi/32) + QPSK(2 ×3pi/32) 11 3 (2n, n: 0~7) 1 (0, 1)  8 PSK QPSK 12 3 (2n, n: 0~7) 1 (0,2) 16 PSK BPSK 13 3 (2n, n: 0~7) 1 (8, 9)  8 PSK QPSK 14 3 (2n, n: 0~7)1 (8, 10) 16 PSK BPSK 15 3 (2n, n: 0~7) 2 (0~3)  8 PSK + 8PSK(2pi/32)QPSK 16 3 (2n, n: 0~7) 2 (0, 1, 4, 5) 16 PSK QPSK 17 3 (2n, n: 0~7) 2(2m, m: 0~3) 32 PSK BPSK 18 3 (2n, n: 0~7) 2 (2m + 8, m: 0~3) 32 PSKBPSK 19 3 (2n, n: 0~7) 3 (0~7) 32 PSK QPSK 20 3 (2n, n: 0~7) 3 (8~15) 32PSK QPSK 21 3 (2n, n: 0~7) 3 (2m, m: 0~7) 32 PSK BPSK 22 3 (2n, n: 0~7)4 (0~15) 32 PSK QPSK 23 4 (0~15) 1 (0, 1) 16 PSK QPSK 24 4 (0~15) 1 (0,2) 32 PSK BPSK 25 4 (0~15) 2 (0~3) 32 PSK QPSK 26 4 (0~15) 2 (0, 1, 4,5) 16 PSK(Overraped) QPSK 27 4 (0~15) 2 (2m, m: 0~3) 32 PSK BPSK 28 4(0~15) 2 (2m + 8, m: 0~3) 32 PSK BPSK 29 4 (0~15) 3 (0~7) 32PSK(Overraped) QPSK 30 4 (0~15) 3 (8~15) 32 PSK QPSK 31 4 (0~15) 3 (2m,m: 0~7) 32 PSK(Overraped) QPSK 32 4 (0~15) 4 (0~15) 32 PSK (Overraped)QPSK 33 4 (0~15) 2 (8, 9, 10, 11) 34 4 (0~15) 2 (0, 1, 8, 9) 35 4 (0~15)2 (0, 2, 9, 10) 36 4 (0~15) 2 (8, 10, 12, 14)

Similar to the above-mentioned scheme, a method for selecting the subsetof a codebook denoted by ‘i1/i2’ may be applied to the codebooksappropriate for Rank-3 to Rank-8 of Tables 13 to 18.

For example, the i2 value of the Rank-3 codebook of Table 13 may becomposed of 16 elements (0˜15), and may be composed of a matrix thatgenerates three orthogonal beams using two vectors. Four types of Rank-3codebooks may be configured using two vectors.

For example, if i2 is composed of 0, 1, 2 and 3, four Rank-3 codebooks(Type-A, Type-B, Type-C and Type-D) may be used, and a detaileddescription thereof will hereinafter be described in detail.

In case of Type-A, a 1^(st) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ⁽³⁾ with anegative(−) co-phase, and a 3^(rd) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾with a negative(−) co-phase. [A: 1^(st) col (W_(8i) ₁ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (−) co-phase), and 3^(rd) col(W_(8i) ₁ ₊₈ ⁽³⁾ with (−) co-phase)].

In case of Type-B, a 1^(st) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ⁽³⁾ with anegative(−) co-phase, and a 3^(rd) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾with a negative(−) co-phase. [B: 1^(st) col (W_(8i) ₁ ₊₈ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (−) co-phase), 3^(rd) col(W_(8i) ₁ ₊₈ ⁽³⁾ with (−) co-phase)].

In case of Type-C, a 1^(st) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾with a positive(+) co-phase, and a 3^(rd) column is composed of W_(8i) ₁₊₈ ⁽³⁾ with a negative(−) co-phase. [C: 1^(st) col (W_(8i) ₁ ⁽³⁾ with(+) co-phase), 2^(nd) col (W_(8i) ₁ ₊₈ ⁽³⁾ with (+) co-phase), 3^(rd)col W_(8i) ₁ ₊₈ ⁽³⁾ with (−) co-phase)].

In case of Type-D, a 1^(st) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, and a 3^(rd) column is composed of W_(8i) ₁ ⁽³⁾with a negative(−) co-phase. [D: 1^(st) col (W_(8i) ₁ ₊₈ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (+) co-phase), 3^(rd) col(W_(8i) ₁ ⁽³⁾ with (−) co-phase)].

In the above-mentioned examples, two vectors for use in the codebook areone vector W_(8i) ₁ ⁽³⁾ and the other vector W_(8i) ₁ ₊₈ ⁽³⁾. In case ofi2=0 and i2=2, the W_(8i) ₁ ⁽³⁾ vector is used for the first column. Incase of i2=1 and i2=3, the W_(8i) ₁ ₊₈ ⁽³⁾ vector is used for the firstcolumn. In addition, in case of i2=0 and i2=1, two different vectors(i.e., W_(8i) ₁ ⁽³⁾ and W_(8i) ₁ ₊₈ ⁽³⁾ vectors) are applied to thesecond and third columns, such that orthogonality may be achievedbetween two columns. On the other hand, in case of i2=2 and i2=3, onevector (i.e., W_(8i) ₁ ⁽³⁾ or W_(8i) ₁ ₊₈ ⁽³⁾ vector) may be applied tothe second and third columns, such that orthogonality may be obtainedusing different co-phase components (i.e., (+) and (−) co-phases).

When comparing one case of (i2=0, 1, 2, 3) at the Rank-3 codebook ofTable 13 with the case of (i2=4, 5, 6, 7) at the Rank-3 codebook ofTable 13, it can be recognized that constituent vectors of the codebookare different from each other. That is, in association with the case of(i2=0, 1, 2, 3), W_(8i) ₁ ⁽³⁾ and W_(8i) ₁ ₊₈ ⁽³⁾ vectors are used. Inassociation with the other case of (i2=4, 5, 6, 7), W_(8i) ₁ ₊₂ ⁽³⁾ andW_(8i) ₁ ₊₀ ⁽³⁾ vectors are used.

By means of the above-mentioned types (Type-A, Type-B, Type-C, andType-D, a Rank-3 codebook generation matrix may also be represented bythe following Table 29.

TABLE 29 I2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 I1 A B C D A B C D A BC D A B C D 0 W_(8i) ₁ ⁽³⁾, W_(8i) ₁ ₊₈ ⁽³⁾ W_(8i) ₁ ₊₂ ⁽³⁾, W_(8i) ₁₊₁₀ ⁽³⁾ W_(8i) ₁ ₊₄ ⁽³⁾, W_(8i) ₁ ₊₁₂ ⁽³⁾ W_(8i) ₁ ₊₆ ⁽³⁾, W_(8i) ₁ ₊₁₄⁽³⁾ 1 W_(8i) ₁ ₊₈ ⁽³⁾, W_(8i) ₁ ₊₁₆ ⁽³⁾ W_(8i) ₁ ₊₁₀ ⁽³⁾, W_(8i) ₁ ₊₁₈⁽³⁾ W_(8i) ₁ ₊₁₂ ⁽³⁾, W_(8i) ₁ ₊₂₀ ⁽³⁾ W_(8i) ₁ ₊₁₄ ⁽³⁾, W_(8i) ₁ ₊₂₂⁽³⁾ 2 W_(8i) ₁ ₊₁₆ ⁽³⁾, W_(8i) ₁ ₊₂₄ ⁽³⁾ W_(8i) ₁ ₊₁₈ ⁽³⁾, W_(8i) ₁ ₊₂₆⁽³⁾ W_(8i) ₁ ₊₂₀ ⁽³⁾, W_(8i) ₁ ₊₂₈ ⁽³⁾ W_(8i) ₁ ₊₂₂ ⁽³⁾, W_(8i) ₁ ₊₃₀⁽³⁾ 3 W_(8i) ₁ ₊₂₄ ⁽³⁾, W_(8i) ₁ ⁽³⁾ W_(8i) ₁ ₊₂₆ ⁽³⁾, W_(8i) ₁ ₊₂ ⁽³⁾W_(8i) ₁ ₊₂₈ ⁽³⁾, W_(8i) ₁ ₊₄ ⁽³⁾ W_(8i) ₁ ₊₃₀ ⁽³⁾, W_(8i) ₁ ₊₆ ⁽³⁾

As a method for reducing the size of bits requisite for codebookindication, the sub-sampling application may be used.

For example, 2 indication bits constructing the Rank-3 codebook may bereduced to exemplary bits shown in Table 30.

TABLE 30 I1 I2 Total bit size 2 4 6 1 4 5 2 3 5 0 4 4 1 3 4 2 2 4

In order to allow the entire bit size for codebook indication to becomposed of 4 bits, three schemes (i.e., i1+i2=0+4, 1+3, 2+2) may beused as necessary. From among the three schemes, if ‘i1’ is composed of0 bit, namely, if ‘i1’ is composed of one element, beam resolution isdeteriorated, resulting in a reduction in performance or throughout.Next, the remaining schemes other than the scheme of using ‘i1’ composedof 0 bit will hereinafter be described in detail.

First, various methods for constructing the i1 subset and the i2 subseton the condition that one bit (1 bit) is assigned to ‘i1’ and 3 bits areassigned to ‘i2’ will hereinafter be described.

In case of selecting/using the subset from among all indexes of i1 andi2, the element of codebook capable of being generated according towhich index is selected is changed to another element, such that it ispreferable that indexes be properly selected to construct ahigh-performance codebook.

If i1 is composed of 1 bit, two indexes may be selected from amongseveral indexes (0, 1, 2, 3) of the i1 composed of 1 bit. The number ofvectors capable of being used as constituent elements of the codebook isset to 12 or 16 according to which index is selected from among indexes(0, 1, 2, 3) of the i1. For example, provided that (0, 1) may beselected from among indexes (0, 1, 2, 3) of the i1, 12 vectors of W_(8i)₁ _(+m) ⁽³⁾ (m=0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22) may be used.In another example, provided that (0, 2) may be selected from amongindexes (0, 1, 2, 3) of the i1, 16 vectors of W_(8i) ₁ _(+m) ⁽³⁾ (m=0,2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30) may be used.That is, if i1 is set to (0, 1) [i.e., i1=(0, 1)], duplicated oroverlapped vectors may be applied to each of i1=0 and i1=1. If i1 is setto (0, 2) [i.e., i1=(0, 2)], different vectors may be applied to each ofi1=0 and i1=2. Therefore, it is preferable that i1=(0, 2) be used fromthe viewpoint of beam resolution.

On the other hand, if i2 is assigned 3 bits, 8 indexes may be selectedfrom among 16 i2 indexes from 0 to 15. A first method for selecting 8indexes is designed to select the i2 index including various vectors soas to increase beam resolution. A second method for selecting 8 indexesperforms index selection to include all of four types (Type-A, Type-B,Type-C, Type-D) constructing a Rank-3 element.

For example, the first method selects two groups from among fouri2-index groups [(0, 1, 2, 3), (4, 5, 6, 7), (8, 9, 10, 11), (12, 13,14, 15)] such that it may use 8 indexes. For example, provided that 8indexes [(0, 2), (4, 6), (8, 10), (12, 14)] are selected as the i2index, Rank-3 codebook elements based on Type-A and Type-C may begenerated using 8 vectors. In another example, provided that 8 indexes[(1, 3), (5, 7), (9, 11), (13, 15)] are selected as the i2 indexes,Rank-3 codebook elements based on Type-B and Type-D may be generatedusing 8 vectors.

For example, the second method may select two groups from among fourgroups [(0, 1, 2, 3), (4, 5, 6, 7), (8, 9, 10, 11), (12, 13, 14, 15)]such that it may use 8 indexes. In case of the matrix constructing aRank-3 codebook, +1 and −1 may be used as co-phase components. Inaddition, there are vectors capable of forming 8 Tx DFT vectors byco-phase components. For example, provided that (+1) is used as theco-phase element in case of vectors numbered 0, 8, 16 and 24, 8 Tx DFTvectors may be formed. In another example, provided that (−1) is used asthe co-phase element in case of vectors numbered 4, 14, 20 and 28, 8 TxDFT vectors may be formed. Considering the co-polarized antennastructure, the use of 8 Tx DFT vectors may achieve high throughput orperformance.

Since the co-phase components used in the matrix constructing the Rank-3codebook are set to (+1) and (−1), it is preferable that the i2 index beselected to include Nos. 0, 8, 16, 4, 14, 20, and 28 vectors capable offorming the 8Tx DFT vector using the above-mentioned co-phasecomponents. For example, (0, 1, 2, 3) and (8, 9, 10, 11) may be selectedas the i2 indexes.

Next, in the case where 2 bits are assigned to ‘i1’ and 2 bits areselected to ‘i2’, various methods for constructing the i2 subset willhereinafter be described in detail. Since i1 includes Nos. 0, 1, 2 and 3indexes, all indexes can be represented through 2 bits.

For example, in order to select the subset of the i2 index when the i2indexes 0 to 15 are classified into four groups [(0, 1, 2, 3), (4, 5, 6,7), (8, 9, 10, 11), and (12, 13, 14, 15)], one group is selected fromamong the four groups so that four elements of the corresponding groupmay be used. One index is selected from among each of the four groupssuch that four elements may be configured. Alternatively, two groups areselected from among four groups, and two indexes are selected from amongthe selected group such that four elements may be configured.

The number of cases, each of which can selectively use two of four types(Type-A, Type-B, Type-C, and Type-D) constructing the Rank-3 codebookelement, is set to 6, respective cases are (A, B), (A, C), (A, D), (B,C), (B, D), and (C, D).

In addition, the number of cases, each of which can selectively use twoof four groups of the i2 index, is set to 6. If the frontmost vectorfrom among the i2 index groups refers to the corresponding group,respective groups may be represented by Nos. 0, 4, 8, and 12 groups.Respective cases, each of which selects two of four groups, are (0, 4),(0, 8), (0, 12), (4, 8), (4, 12), and (8, 12).

As a combination of six cases about a method for constructing the Rank-3codebook element and six cases about a method for selecting a vectorgroup, a method for constructing subsets of a total of 36 i2 indexes isachieved.

According to the above-mentioned examples, in the case where, inassociation with the Rank-3 codebook, one bit is assigned to ‘i1’ and 3bits are assigned to ‘i2’, and 2 bits are assigned to ‘i1’ and 2 bitsare assigned to ‘i2’, examples constructing the i2 and i2 subsets may berepresented by the following Table 31.

TABLE 31 i1 i2 Bit (index) Bit (index) 1 (0, 1) 3 (0, 2) (4, 6) (8, 10)(12, 14) 1 (0, 1) 3 (1, 3) (5, 7) (9, 11) (13, 15) 1 (0, 1) 3 (0, 1) (4,5) (8, 9) (12, 13) 1 (0, 1) 3 (2, 3) (6, 7) (10, 11) (14, 15) 1 (0, 1) 3(0, 1, 2, 3) (8, 9, 10, 11) 1 (0, 1) 3 (0, 1, 2, 3) (4, 5, 6, 7) 1(0, 1) 3 (4, 5, 6, 7) (12, 13, 14, 15) 1 (0, 2) 3 (0, 2) (4, 6) (8, 10)(12, 14) 1 (0, 2) 3 (1, 3) (5, 7) (9, 11) (13, 15) 1 (0, 2) 3 (0, 1) (4,5) (8, 9) (12, 13) 1 (0, 2) 3 (2, 3) (6, 7) (10, 11) (14, 15) 1 (0, 2) 3(0, 1, 2, 3) (8, 9, 10, 11) 1 (0, 2) 3 (0, 1, 2, 3) (4, 5, 6, 7) 1 (0,2) 3 (4, 5, 6, 7) (12, 13, 14, 15) 2 (0, 1, 2, 3) 2 (0, 1, 2, 3) 2 (0,1, 2, 3) 2 (4, 5, 6, 7) 2 (0, 1, 2, 3) 2 (8, 9, 10, 11) 2 (0, 1, 2, 3) 2(12, 13, 14, 15) 2 (0, 1, 2, 3) 2 (0, 4, 8, 12) 2 (0, 1, 2, 3) 2 (1, 5,9, 13) 2 (0, 1, 2, 3) 2 (2, 6, 10, 14) 2 (0, 1, 2, 3) 2 (3, 7, 11, 15) 2(0, 1, 2, 3) 2 (0, 2, 4, 6) 2 (0, 1, 2, 3) 2 (0, 2, 8, 9) 2 (0, 1, 2, 3)2 (1, 3, 5, 7) 2 (0, 1, 2, 3) 2 (1, 3, 10, 11)

Even in the case where the Rank-4 codebook is configured, the followingsubsampling may be used. For example, two indicators (i1 and i2)constructing the above-mentioned Rank-3 codebook may be reduced as shownin the following Table 32.

TABLE 32 I1 I2 Total bit size 2 3 5 1 3 4 2 2 4

In association with the Rank-4 codebook, the subsets of the i1 and i2indexes can be selected in a similar way to the scheme for selecting thesubset from among the above-mentioned Rank-3 codebook. The same partsmay herein be omitted for convenience and clarity of description.

In the Rank-4 codebook, in case that one bit is assigned to ‘i1’ and 3bits are assigned to ‘i2’, and in another case that 2 bits are assignedto ‘i1’ and 2 bits are assigned to ‘i2’, examples for constructing thei2 subset and the i2 subset can be represented by the following Table33.

TABLE 33 i1 i2 Bit (index) Bit (index) 1 (0, 1) 3 1 (0, 2) 3 2 (0, 1, 2,3) 2 (0, 1, 2, 3) 2 (0, 1, 2, 3) 2 (4, 5, 6, 7) 2 (0, 1, 2, 3) 2 (0, 1,4, 5) 2 (0, 1, 2, 3) 2 (2, 3, 6, 7) 2 (0, 1, 2, 3) 2 (0, 2, 4, 6) 2 (0,1, 2, 3) 2 (1, 3, 5, 7)

On the other hand, the selected codebook subset may be used to reportPUSCH. For example, during the mode for reporting a PMI for each subbandas shown in the PUSCH report mode 1-2, the i1 and i2 subsets may be usedto reduce PMI feedback overhead. In this case, in association with ‘i1’,one index may be reported at WB, and in association with ‘i2’, indexesfor each SB may be reported.

In addition, the 3GPP LTE Release-10 system may use a specific mode forreporting SB CQI and SB PMI as a new PUSCH report mode. Even in theabove-mentioned report mode, the codebook subset may be used to reducethe number of report bits for indicating the codebook. In this case, inassociation with ‘i1’, one index may be reported at WB, and inassociation with ‘i2’, indexes for each SB may be reported.

Exemplary PUCCH Report Modes

First of all, during periodic CQI/PMI/RI transmission, CQI, CQI/PMI,preferred subband selection and CQI information may be calculated on thebasis of the last reported periodic RI, and subband selection and a CQIvalue may be calculated on the basis of the last reported periodic WBPMI and RI. In addition, two precoder indexes (I1 and I2) may bereported at different time points or at the same time point. Consideringthe above-mentioned situation, for example, the report modes shown inTable 34 may be considered for feedback information transmission.

TABLE 34 T1 T2 T3 Mode 1-1-1 (RI + I1)_WB (I2 + CQI)_WB Mode 1-1-2(RI)_WB (I1 + I2 + CQI)_WB Mode Mode 2-1(1) (RI + PTI(0)) (I1)_WB (I2 +2-1 CQI)_WB Mode 2-1(2) (RI + PTI(1)) (I2 + CQI)_WB (I2 + CQI)_SB

In Table 34, I1 and I2 may indicate indexes of the codebook composed ofprecoder elements, and PTI may indicate a precoder type indication bit.

In Mode 1-1-1 shown in Table 34, the precoder index I1 may indicate aprecoder index that is calculated/selected on the basis of RItransmitted in a current subframe. The precoder index I2 may indicate aprecoder index that is calculated/selected on the basis of the lastreported RI and the last reported I1. CQI may indicate a value that iscalculated on the basis of the last reported RI, the last reported I1,and the current reported I2.

In Mode 1-1-2 shown in Table 34, the precoder indexes I1 and I2 mayindicate precoder indexes that are calculated/selected on the basis ofthe last reported RI. CQI may indicate a value that is calculated on thebasis of the last reported RI and the current reported I1 and I2.

In Mode 2-1(1) shown in Table 34, the precoder index I1 may indicate aprecoder index that is calculated/selected on the basis of the lastreported RI. The precoder index I2 may indicate a precoder index that iscalculated/selected on the basis of the last reported RI and the lastreported I1. CQI may indicate a value that is calculated on the basis ofthe last reported RI, the last reported I1 and the current reported I2.When (I1) and (I2+CQI) are reported between (RI+PTI) transmissioncycles, (I1) may be reported only once and (I2+CQI) may be reportedseveral times. Alternatively, when (I1) and (I2+CQI) are reportedbetween (RI+PTI) transmission cycles, (I1) may be reported two times and(I2+CQI) may be reported several times. In another example, (I1) may besuccessively reported as necessary, or (I1) and (I2+CQI) may bealternately reported. Otherwise, (I1) may be reported just after the(RI+PTI) report time, or may be reported just before the next (RI+PTI)report time.

In Mode 2-1(2) shown in Table 34, the precoder index I2 may indicate aprecoder index that is calculated/selected on the basis of the lastreported RI. The precoder index I2 may indicate a precoder index that iscalculated/selected on the basis of the last reported RI and the lastreported I1. SB CQI and SB I2 may indicate a value and indexcalculated/selected on the basis of the last reported RI and the lastreported I1.

Mode 2-1 shown in Table 34 will hereinafter be described in detail.

Mode 2-1 [Mode 2-1(1) and Mode 2-1(2)] shown in Table 34 may correspondto a report mode configured in an extended form of the PUCCH report mode2-1 shown in Table 5. The PUCCH report mode 201 shown in Table 5 may bea PUCCH report mode defined in the 3GPP LTE Release-8/9 system, and isdefined as a mode for reporting WB PMI/CQI and SB CQI. In this case, SBCQI may be a CQI of an SB selected from among a BP. The term “BP” mayindicate the subset of the system bandwidth. BP defined in the systembandwidth is cyclically selected in the order of time such that a CQI ofthe BP can be reported and a plurality of SB CQIs can also be reported.In other words, RI/PMI/CQI can be reported in the same time order of(RI)→(WB PMI/CQI)→(SB CQI at first BP)→(SB CQI at second BP)→ . . . →(SBCQI at n-th BP). In this case, if the report cycle and offset of PMI/CQIare determined through RRC signaling, WB PMI/CQI and SB CQI may bereported in response to the set report cycle. RI may be established tohave a cycle corresponding to an integer multiple on the basis of thereport cycle of WB PMI/CQI. Compared to WB PMI/CQI transmission time, RImay be reported prior to a subframe corresponding to the set offsetusing the offset indicator.

For the PUCCH report mode for use in the system (e.g., 3GPP LTERelease-9 system) supporting the extended antenna structure, theextended report mode of the PUCCH report mode 2-1 shown in Table 5 maybe defined.

As the CQI/PMI/RI feedback types of the PUCCH report mode for use in the3GPP LTE Release-8/9 system, four feedback types (Type-1, Type-2,Type-3, Type-4) may be defined. Type-1 is a CQI feedback for aUE-selected subband, Type-2 is a WB CQI feedback and a WB PMI feedback,Type-3 is an RI feedback, and Type-4 is a WB CQI feedback. Similar tothe above-mentioned four types, four CQI/PMI/RI feedback types for usein the PUCCH report mode of the 3GPP LTE Release-10 system may bedefined. For example, Report Type 1 is an RI/PTI feedback, Report Type 2is a WB I1 feedback, Report Type 3 is a WB I1/CQI feedback, and ReportType 4 is an SB I2/CQI feedback. According to the Type-1 PTI setup, areport type may be decided. For example, if Type-1 PTI is set to zero(PTI=0), Type-1, Type-2 and Type-3 may be used for such report. IfType-1 PTI is set to 1 (PTI=1), Type-1, Type-3 and Type-4 may be usedfor such report. Accordingly, Mode 2-1(1) and Mode 2-1(2) shown in Table34 may be defined.

If the precoder element is indicated using one precoder index in thesame manner as in 2Tx antenna transmission or 4Tx antenna transmission,PTI is always set to 1, such that Type-1, Type-3, and Type-4 may be usedfor the report. Differently from the report scheme for use in the 3GPPLTE Release-8/9 system, SB PMI/CQI may be transmitted at Type-4. Inorder to enable Type-4 transmission for the 3GPP LTE Release-10 systemto operate similarly to the 3GPP LTE Release-8/9 system, one or more BPswithin the system bandwidth may be cyclically reported, and PMI/CQI fora preferred SB within BP(s) may be reported. In this case, the Type-3 orType-4 report cycle may be determined in the same manner as in thePMI/CQI cycle setup of the 3GPP LTE Release-8/9 system. For example,Type-3 and Type-4 may be reported according to a cycle set for PMI/CQI.In addition, a cycle for Type-1 can also be determined in the samemanner as in an RI cycle setup for the 3GPP LTE Release-8/9 system. Forexample, the Type-1 report cycle may be denoted by an integer multipleof the Type-3 report cycle. In addition, an offset value may beestablished in such a manner that Type-1 can be transmitted at asubframe located before a Type-3 report subframe by a predetermineddistance corresponding to a predetermined number of subframes.

On the other hand, when the precoder element is indicated using twoprecoder indexes as in 8Tx antenna transmission, (Type 1-Type 2-Type 3)or (Type 1-Type 3-Type 4) may be reported according to the PTI value.When the set of two feedback types is selected according to the PTIvalue, the report cycle for individual feedback types must be decided.

Subsampling of PUCCH report modes will hereinafter be described indetail. PUCCH Report Mode-A and PUCCH Report Mode-B corresponding to theextended version of PUCCH Report Mode Mode 1-1 will hereinafter bedescribed.

In the case where no codebook sampling is applied to PUCCH Report Mode-Aand PUCCH Report Mode-B, feedback overhead (i.e., the number ofrequested bits) for report types may be summarized according to Rankvalues as shown in Table 35.

TABLE 35 PUCCH Mode-A Type-5 PUCCH Mode-B reporting Type-2a Type-3Type-2b (Joint of RI reporting reporting reporting Rank and W1) (W2 +CQI) (RI) (W1 + W2 + CQI) 1 6  8 (4 + 4) 3 12 (4 + 4 + 4) 2 11 (4 + [4 +3]) 15 (4 + 4 + [4 + 3]) 3 11 (4 + [4 + 3]) 13 (2 + 4 + [4 + 3]) 4 10(3 + [4 + 3]) 12 (2 + 3 + [4 + 3]) 5  7 (0 + [4 + 3])  9 (2 + 0 + [4 +3]) 6  7 (0 + [4 + 3])  9 (2 + 0 + [4 + 3]) 7  7 (0 + [4 + 3])  9 (2 +0 + [4 + 3]) 8  7 (0 + [4 + 3])  7 (0 + 0 + [4 + 3])

In Table 35, some Type-2 Reports for PUCCH Mode-B exceed 11 bits, suchthat they can also exceed the limitation of PUCCH transmission bit.Therefore, codebook subsampling may be applied to Type-2 Report at PUCCHMode-B as shown in Table 36.

TABLE 36 PUCCH Mode-B Type-3 Type-2b reporting reporting Rank RI (W1 +W2 + CQI) 1 3 11 (4 + 3 + 4) W1: All, W2: 0~7 32 PSK DFT vector (nooverlapped) QPSK co-phasing 2 11 (3 + 1 + [4 + 3]) W1: 2n(n: 0~7), W2:0, 4 16 PSK DFT vector (no overlapped) BPSK co-phasing 3 11 (1 + 3 +[4 + 3]) W1: 0, 2, W2: 16 PSK DFT vector 2m(m: 0~7) (no overlapped) Twotypes of W(3) 4 11 (1 + 3 + [4 + 3]) W1: 0, 2, W2: All 16 PSK DFT vector(no overlapped) QPSK co-phasing 5  9 (2 + 0 + [4 + 3]) W1: All 16 PSKDFT vector (no overlapped) BPSK co-phasing 6  9 (2 + 0 + [4 + 3]) W1:All 16 PSK DFT vector (no overlapped) BPSK co-phasing 7  9 (2 + 0 + [4 +3]) W1: All 16 PSK DFT vector (no overlapped) BPSK co-phasing 8  7 (0 +0 + [4 + 3]) QPSK DFT vector (no overlapped) BPSK co-phasing

As can be seen from Table 35, Type-2a Report does not exceed 11 bitssuch that subsampling need not be used, and Type-5 Report may requirebits, the number of which is double that of Type-3 Report. Since Type-5and Type-3 Reports carry rank information, the Type-5 and Type-3 typesshould have robust reliability. In the case where rank information hashigh priority for PUCCH report and several types need to be reported inthe same subframe, CQI and PMI may drop from the RI transmissionsubframe. Considering the above-mentioned problem, the codebooksubsampling may also be applied to Type-3 Report so as to increase thereliability of rank feedback.

Applying the subsampling to Type-5 Report may be represented, forexample, by Tables 37 to 40. Tables 37 and 38 show the exemplary casesof the maximum Rank-2. Table 39 shows the exemplary case of the maximumRank-4. Table 40 shows the exemplary case of the maximum Rank-8.

TABLE 37 PUCCH Mode-A Type-5 reporting Type-2a Joint of RI reportingRank and W1 (W2 + CQI) 1 5 (1 + 4)  8 (4 + 4) W1: All, non-overlapped 32W2: All oversampled beam QPSK co-phasing 2 11 (4 + [4 + 3])non-overlapped 32 oversampled beam QPSK co-phasing

TABLE 38 PUCCH Mode-A Type-5 reporting Type-2a reporting Rank Joint ofRI and W1 (W2 + CQI) 1 4  8 (4 + 4) W1: 2n (n: 0~7), W2: All 2 (log2(8 +8)) 11 (4 + [4 + 3])

TABLE 39 PUCCH Mode-A Type-5 reporting Type-2a Joint of RI reportingRank and W1 (W2 + CQI) 1 5 (2 + 3) 8 (4 + 4) W1: 2n (n: 0~7),non-overlapped 32 W2: All oversampled beam QPSK co-phasing 2 11non-overlapped 32 (4 + [4 + 3]) oversampled beam QPSK co-phasing 3 11W1: All, W2: All non-overlapped 16 (4 + [4 + 3]) oversampled beam Twotypes of W(3) 4 10 non-overlapped 16 (3 + [4 + 3]) oversampled beam QPSKco-phasing

TABLE 40 PUCCH Mode-A Type-5 reporting Type-2a Joint of RI reportingRank and W1 (W2 + CQI) 1 5 (3 + 2) 8 (4 + 4) W1: 4n (n: 0~3), QPSKco-phasing 2 11 W2: All QPSK co-phasing (4 + [4 + 3]) 3 11 W1: All, W2:All 16 PSK DFT vector (4 + [4 + 3]) (overlapped) Two types of W(3) 4 1016 PSK DFT vector (3 + [4 + 3]) (no overlapped) QPSK co-phasing 5 7 16PSK DFT vector (0 + [4 + 3]) (no overlapped) BPSK co-phasing 6 7 16 PSKDFT vector (0 + [4 + 3]) (no overlapped) BPSK co-phasing 7 7 16 PSK DFTvector (0 + [4 + 3]) (no overlapped) BPSK co-phasing 8 7 QPSK DFT vector(0 + [4 + 3]) (no overlapped) BPSK co-phasing

In the example of Table 37, Type-5 bits for RI may be fixed to 5 bits,and W1 may be used as the fullset, resulting in increased systemperformance or throughput.

In the example of Table 38, Type-5 bits for RI may be used as 4 bits,such that RI can be transmitted much more robustly than the example ofTable 36. On the other hand, since the subsampled W1 instead of thefullset of W1 is used, system performance or throughput of Table 38 islower than that of Table 36. Meanwhile, as can be seen from Tables 38,39 and 40, W1 and W2 of Rank-1 are identical to those of Rank-2irrespective of the maximum rank, resulting in the implementation ofnested characteristics.

Compared to the above-mentioned PUCCH Mode-A and PUCCH Mode-B, co-phaseproperty can be maintained by the codebook subsampling for the PUCCHMode-A, and at the same time beam granularity can be reduced. On theother hand, while more precise beam granularity than PUCCH Mode-A isprovided by the codebook subsampling for PUCCH Mode-B, the co-phaseproperty is unavoidably deteriorated.

PUCCH Report Mode-C corresponding to the extended version of the legacyPUCCH report mode 2-1 will hereinafter be described in detail.

Feedback overhead (the number of feedback bits) requested for PUCCHMode-C can be represented by the following Table 41.

TABLE 41 PUCCH Mode-C (PTI = 0) PUCCH Mode-C (PTI = 1) Type-6 Type-7Type-2a Type-6 Type-2a Type-8 reporting reporting reporting reportingreporting reporting Rank (RI + PTI) W1 (wb-W2 + CQI) (RI + PTI) (wb-W2 +wb-CQ1) (sb-W2 + sb-CQI + L-bit) 1 4 (3 + 1) 4 8 (4 + 4) 4 (3 + 1) 8(4 + 4) 10 (4 + 4 + 2) 2 4 11 (4 + [4 + 3])  11 (4 + [4 + 3])  13 (4 +[4 + 3] + 2)  3 2 11 (4 + [4 + 3])  11 (4 + [4 + 3])  13 (4 + [4 + 3] +2)  4 2 10 (3 + [4 + 3])  10 (3 + [4 + 3])  12 (3 + [4 + 3] + 2)  5 2 7(0 + [4 + 3]) 7 (0 + [4 + 3]) 9 (0 + [4 + 3] + 2) 6 2 7 (0 + [4 + 3]) 7(0 + [4 + 3]) 9 (0 + [4 + 3] + 2) 7 2 7 (0 + [4 + 3]) 7 (0 + [4 + 3]) 9(0 + [4 + 3] + 2) 8 2 7 (0 + [4 + 3]) 7 (0 + [4 + 3]) 9 (0 + [4 + 3] +2)

As can be seen from Table 41, if PTI is set to 1 (i.e., PTI=1) forType-6 Report, bits required for Type-8 Report at Ranks 2 to 4 exceed 11bits, such that the codebook subsampling may be applied to the exceededbits. The principle similar to that of the codebook subsampling used forthe above-mentioned PUCCH Mode-B may be applied to W2 of Type-8. Inaddition, as shown in Table 41, RI feedback reliability of PUCCH Mode-Cmay be lower than that of the above-mentioned PUCCH Mode-B because ofthe PTI indication of one bit. In addition, the duty cycle of the W1report is longer than the duty cycle of RI. Considering this property,the report time points and priorities of the reported types may bedetermined.

Embodiment 3

Embodiment 3 shows the codebook subsampling method that is capable ofbeing applied to PUCCH report modes. As the extended version of thelegacy PUCCH report mode of the system (e.g., 3GPP LTE Release-10system) supporting the extended antenna structure, three PUCCH reportmodes [(Mode 1-1-1, Mode 1-1-2, Mode 2-1) or (Mode-A, Mode-B, Mode-C)]shown in Table 39 may be applied.

Mode 1-1-1 reports the joint coded RI and I1, and reports the widebandCQI and the wideband I2. Mode 1-1-2 is a mode for transmitting (RI)_WBand (I1+I2+CQI)_WB. Mode 2-1 may transmit different feedbackinformation. If PTI is set to zero (PTI=0), (RI+PTI(0)), (I1)_WB, and(I2+CQI)_WB may be transmitted. If PTI is set to 1 (PTI=1), (RI+PTI(1)),(I2+CQI)_WB, and (I2+CQI)_SB can be transmitted. On the other hand, inthe present embodiments, two precoder indexes I1 and I2 may also berepresented by W1 and W2, respectively.

A method for implementing report bandwidth optimization by applying thecodebook subsampling to each PUCCH report mode and at the same timemaintaining the PUCCH feedback coverage as in the legacy 3GPP LTERelease-8/9 will hereinafter be described in detail.

Signaling overhead requested for PUCCH Report Modes 1-1-1 and 1-1-2 areshown in Table 35. In Table 35, Mode-A corresponds to PUCCH Report Mode1-1-1, and Mode-B corresponds to PUCCH Report Mode 1-1-2.

As can be seen from Table 35, 6 bits are needed for Type-5 (joint codedRI and WI) at PUCCH Report Mode 1-1-1. Since 6 bits are assigned to RIand WI because of the joint-coded RI and WI, coverage for RItransmission is greatly lower than that of the legacy 3GPP LTE Release-8system. As a result, RI detection failure or performance deteriorationmay be encountered. Therefore, WI subsampling may be used to increase RIcoverage. In Mode 1-1-1, Type-2a (W2 and CQI) Report may be morefrequently updated than Type-5 Report, such that it can be recognizedthat Type-2a need not always be protected. Therefore, in so far as thereported bandwidth does not exceed the size of one bit, W2 sampling neednot be used.

In PUCCH Report Mode 1-1-2, RI is not joint-coded with other CSIinformation, such that RI coverage can be maintained in the same manneras in the legacy 3GPP LTE Release-8 system. However, as shown in Table39, in case of Rank-1, Rank-2, Rank-3, and Rank-4, signaling overheadexceeding 11 bits are required for Type-2b (W1+W2+CQI) Report.Therefore, in order to reuse PUCCH format 2 of the 3GPP LTE Release-8system, codebook sampling is needed.

First, the subsampling method capable of being applied to PUCCH ReportMode 1-1-1 will hereinafter be described in detail.

W1 candidates may be different in number according to transmissionranks. That is, as shown in Tables 11 to 18, the number of W1 candidatesmay be set to 16, 16, 4, 4, 4, 4, 4, and 1 for Ranks 1 to 8,respectively. If RI and W1 are joint-coded and reported, the requestedsignaling overhead is denoted by 6 bits (=ceiling(log 2(53))). In orderto extend the RI coverage, signaling overhead may be reduced to 4 or 5bits through W1 subsampling. Examples of the W1 subsampling are shown inthe following Table 42.

TABLE 42 Alternative W1 Alt-1 Rank-1 and 2 8 elements for each rank: (0,2, 4, 6, 8, 10, 12, 14) Rank-3 and 4 4 elements for each rank: (0, 1, 2,3) Rank-5, 6 and 7 2 elements for each rank: (0, 1) Rank-8 1 element:(0) Total number of 31 elements (5 bit) element Alt-2 Rank-1 and 2 4elements for each rank: (0, 4, 8, 12) Rank-3 and 4 2 elements for eachrank: (0, 2) Rank-5, 6, 7 and 8 1 elements for each rank: (0) Totalnumber of 16 elements (4 bit) element

In the dual-stage codebook structure, overlapped beams are presentbetween beam groups. As can be seen from the Alt-1 scheme of Table 42,although subsampling is applied to W1 by excluding only the odd W1values from the codebook, all the beams of the codebook can bemaintained. However, W1 and W2 for constructing the entire codebook aretransmitted from other subframes, such that performance deteriorationmay occur as compared to the use of the entire codebook to which nosubsampling is applied. Meanwhile, as can be seen from the Alt-2 schemeof Table 42, if subsampling capable of excluding many more beams fromthe codebook is applied, it is impossible to use some beams of thecodebook differently from the Alt-1 scheme in which all beams of thecodebook can be maintained, resulting in the occurrence of performancedeterioration.

Table 43 shows, in the 8×2 SU-MIMO transmission, the system levelperformance of PUCCH Report Mode 1-1-1 based on the codebook subsamplingapplication. Table 43 shows that, under the condition that (4+4) is usedas W1 and W2 bits for Rank-1 and Rank-2 and the Alt-1 and Alt-2 schemesare applied thereto, an average spectral efficiency (SE) and a cell-edgeSE for a cross-polarized antenna structure and a co-polarized antennastructure. While the Alt-1 scheme of Table 43 generates marginalperformance deterioration in all of the average SE and the cell-edge SE,the Alt-2 scheme generates relatively high performance deterioration inthe cell-edge SE.

TABLE 43 Cross-polarized (4 λ) Co-polarized (0.5 λ) Antenna AntennaFeedback information Average Cell Edge Average Cell Edge (W1 + W2 forrank-1, SE SE SE SE W1 + W2 for rank-2) (bps/Hz) (bps/Hz) (bps/Hz)(bps/Hz) Reference (4 + 4, 4 + 4) 1.63 0.0436 1.72 0.0730  (0.00%)(0.00%)  (0.00%) (0.00%) Alt-1 (3 + 4, 3 + 4) 1.59 0.0436 1.71 0.0730(−2.00%) (0.00%) (−1.00%) (0.00%) Alt-2 (2 + 4, 2 + 4) 1.59 0.0404 1.680.0714 (−2.00%) (−7.00%)  (−2.00%) (−2.00%) 

As can be seen from Table 43, while the subsampled codebook of 5 bitsmaintains system performance, the other subsampled codebook of 4 bitsreduces the system performance by a predetermined amount correspondingto a maximum of 7%. Therefore, although RI coverage of the Alt-1 schemeis relatively lower than that of the Alt-2 scheme, the Alt-1 scheme ismore preferable than the Alt-2 scheme from the viewpoint of systemperformance.

Hereinafter, the subsampling method capable of being applied to PUCCHReport Mode 1-1-2 will be described in detail.

In the (W1+W2+CQI) report of PUCCH Report Mode 1-1-2, W1 and W2 arereported in the same subframe. Therefore, subsampling may be used tomaintain the report bandwidth of 11 bits or less. As described above, incase of the subsampling for reducing the W1 value by 1 bit (for example,in the case where 8 index subsets are selected from among 16 indexes),all the beams of the codebook can be maintained, such that systemperformance deterioration can be minimized. However, if the W1 value issubsampled by bits of more than 1 bit, a specific-directional beam groupis excluded from the codebook, such that system performance may begreatly deteriorated. Therefore, it may be preferable that, inassociation with Rank-2 to Rank-4, 1-bit subsampling is performed at W1and more bits are excluded at W2.

The following Table 44 shows exemplary subsampling methods capable ofbeing applied to PUCCH Report Mode 1-1-2.

TABLE 44 Alt W1 W2 Alt-1 Rank1 3 bit: 4 bit: (0, 2, 4, 6, 8, 10, 12, 14)(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15) Rank2 3 bit: 1bit: (0, 2, 4, 6, 8, 10, 12, 14) (0, 1) Rank3 1 bit: 3 bit: (0, 2) (0,2, 4, 6, 8, 10, 12, 14) Rank4 1 bit: 3 bit: (0, 2) (0, 1, 2, 3, 4, 5, 6,7) Rank5~7 2 bit 0 bit Rank8 0 bit 0 bit Alt-2 Rank1 3 bit: 2 bit: (0,2, 4, 6, 8, 10, 12, 14) (0, 1, 2, 3) Rank2 3 bit: 1 bit: (0, 2, 4, 6, 8,10, 12, 14) (0, 1) Rank3 1 bit: 3 bit: (0, 2) (0, 2, 4, 6, 8, 10, 12,14) Rank4 1 bit: 3 bit: (0, 2) (0, 1, 2, 3, 4, 5, 6, 7) Rank5~7 2 bit 0bit Rank8 0 bit 0 bit

Referring to Table 44, according to the Alt-1 scheme and the Alt-2scheme, only one bit is reduced at W1 for Rank-1 to Rank-4 so as toprevent all the beam groups from being lost. Therefore, W2 is subsampledaccording to the requested bandwidth.

Table 45 shows, in the 8×2 SU-MIMO transmission, the system levelperformance of PUCCH Report Mode 1-1-1 based on the codebook subsamplingapplication. Table 45 shows that, under the condition that (4+4) is usedas W1 and W2 bits for Rank-1 and Rank-2 and the Alt-1 and Alt-2 schemesare applied thereto, an average spectral efficiency (SE) and a cell-edgeSE for a cross-polarized antenna structure and a co-polarized antennastructure.

TABLE 45 Cross-polarized (4 λ) Co-polarized (0.5 λ) Feedback AntennaAntenna information Average Cell Edge Average Cell Edge (W1 + W2 forrank-1, SE SE SE SE W1 + W2 for rank-2) (bps/Hz) (bps/Hz) (bps/Hz)(bps/Hz) Reference (4 + 4, 4 + 4) 1.63 0.0416 1.72 0.0736  (0.00%)(0.00%)  (0.00%)  (0.00%) Alt-1 (3 + 4, 3 + 1) 1.60 0.0416 1.68 0.0708(−2.00%) (0.00%) (−2.00%) (−4.00%) Alt-2 (3 + 2, 3 + 1) 1.58 0.0416 1.660.0698 (−3.00%) (0.00%) (−3.00%) (−5.00%)

As can be seen from Table 45, some steering vectors of 8 Tx antennas areexcluded from W2 subsampling, such that performance deterioration of theco-polarized antenna structure is relatively larger than that of thecross-polarized antenna structure. On the other hand, there arisesmarginal performance deterioration in the cross-polarized antennastructure.

Therefore, it can be recognized that performance deterioration caused bythe use of subsampled codebook under the condition that W1 subsampled by3 bits is used can be accommodated. Therefore, it is preferable that theAlt-1 scheme is applied to PUCCH Report Mode 1-1-2.

Hereinafter, the subsampling scheme capable of being applied to PUCCHReport Mode 2-1 will be described in detail.

In PUCCH Report Mode 2-1, four report types [(RI+PTI), (W1)_WB,(W2+CQI)_WB, (W2+CQI)_SB)] may be fed back. Each report type may bechanged according to PTI selection. Table 41 shows signaling overheadrequired for each report type in case of PUCCH Mode 2-1 (denoted byMode-C in Table 45). It is assumed that, in case of the (W2+CQI)_SBreport at PTI=1, an L-bit indicator for a UE-selected subband iscontained in Table 41.

In Table 41, in case of Rank-2, Rank-3, and Rank-3 on the condition thatPTI=1 is indicated, overhead required for reporting the L-bit indicatorfor each of (W2+CQI)_SB and SB exceeds 11 bits. Associated signalingoverhead must be reduced such that PUCCH Format 2 of the 3GPP LTERelease-8 can be reused. In order to reduce the signaling overhead, thefollowing two methods (Option 1 and Option 2) can be used. Option 1 cannewly define a predetermined SB cycling without using the selected bandindicator of L bits. Option 2 performs W2 subsampling such that theL-bit selected band indicator can be reused.

In case of Option 1, SB CQI and SB W2 may be reported through PUCCHFormat 2. However, according to Option 1, a CQI report cycle for eachsubband is increased, such that performance deterioration can be moresensitively generated at a time-selective channel using the predefinedSB period. In addition, WB CQI and WB W2 should be reported between theperiods of BP (Bandwidth Part) report duration, such that the CQI reportcycle at each subband can be largely increased, resulting in increasedperformance deterioration.

In case of Option 2, SB CQI and SB W2 are reported along with the L-bitselected bandwidth indicator, such that the number of bits required forperforming such report at Rank-2, Rank-3, and Rank-4 exceeds a specificvalue of 11. Therefore, W2 subsampling can be applied, and Table 46shows the example of W2 subsampling.

TABLE 46 Alternative W2 Rank-1 2 bit: (0, 1, 2, 3) Rank-2 2 bit: (0, 1,8, 9) Rank-3 2 bit: (0, 2, 8, 10) Rank-4 2 bit: (0, 1, 4, 5) Rank-5~8 0bit

Table 47 shows, in the 8×2 SU-MIMO transmission, the system levelperformance of PUCCH Report Mode 2-1 for use in Option 1 and Option 2.Table 47 shows that, in case of two methods (Option 1 and Option 2), anaverage spectral efficiency (SE) and a cell-edge SE for across-polarized antenna structure and a co-polarized antenna structure.It is assumed that, in order to measure system performance, SB CQI andSB W2 are reported at every report cycle of 5 ms, and WB W1 is updatedat intervals of 45 ms. In addition, it is assumed that 2-bit subsampledW2 is applied to Option 2.

TABLE 47 Cross-polarized (4 λ) Co-polarized (0.5 λ) Antenna AntennaFeedback Average Cell Edge Average Cell Edge information SE SE SE SE(W1 + W2 for rank-1) (bps/Hz) (bps/Hz) (bps/Hz) (bps/Hz) Option-1: 1.630.0472 2.24 0.0892 Predefined cycling  (0.00%) (0.00%)  (0.00%)  (0.00%)(4 + 4) Option-2: 1.70 0.0480 2.30 0.0896 UE band selection (4.00%)(1.00%) (3.00%) (0.00%) with W2 subsampling (4 + 2)

As can be seen from Table 47, the average SE of Option 1 is lower thanthat of Option 2 by a system performance deterioration of 3% to 4%,because the report operation period of WB CQI/WB W2 for Option 1 islonger than that of Option 2. For example, in the same manner as in thepredefined SB cycling at the system bandwidth of 5 MHz, Option 1 reportsCSIs of all subbands, such that the report cycle of WB CQI/WB W2 islonger than that of Option 2.

As described above, Option 2 has higher performance than Option 1, suchthat it is preferable that an L-bit indicator for a UE-selected band isincluded and W2 subsampling is applied to Option 2 in terms of systemperformance. In addition, the UE band selection function has alreadybeen used in the legacy system (3GPP LTE Release-8 system), such thatcomplexity for Option 2 implementation is also reduced.

Therefore, according to the inventive codebook subsampling schemeapplied to each PUCCH mode, the legacy PUCCH format 2 is reused andsystem performance deterioration can be minimized.

On the other hand, Table 48 shows parameters applied to simulation ofsystem performances shown in Tables 43, 45, and 47. In addition, Tables49, 50 and 51 show parameters applied to simulations of systemperformances of PUCCH Format 1-1-1, PUCCH Format 1-1-2, and PUCCH Format2-1.

TABLE 48 Parameter Assumption Number of cells 57 Deployment model Hexgrid, 3 sector sites Inter site distance 200 m Average number of UEs percell 10 Traffic model Full buffer UE speeds of interest 3 km/h Bandwidth5 MHz Carrier frequency 2.5 GHz Control OFDM symbols per RB 3 pair Maxnumber of HARQ 5 retransmissions Channel model ITU Urban Micro BSantenna configuration Two closely spaced ±45° cross-poles with 0.5 λseparation ULA with 0.5 λ separation and vertical polarization UEantenna configuration 2 Rx: cross-polarized 0°/90°, 0.5 λ separationReceiver MMSE with no inter-cell interference suppression SchedulerProportional fair in time and frequency Channel estimation Perfectchannel estimation Outer-loop link adaptation Yes Target BLER 10% Numberof RBs per subband 4 RBs Number of Subband 8 Number of Bandwidth part 2Frequency granularity for CQI 4 RBs reporting Feedback delay 5 msFeedback codebook for 8Tx LTE-A 8Tx codebook transmission

TABLE 49 RI reporting periodicity 20 ms CQI reporting periodicity/  5ms/Wideband frequency granularity PMI reporting W1 20 ms/Widebandperiodicity/ frequency granularity PMI reporting W2  5 ms/Widebandperiodicity/ frequency granularity Transmission mode SU-MIMO (Rankadaptation - up to Rank- 2)

TABLE 50 RI reporting periodicity 20 ms CQI reporting periodicity/  5ms/Wideband frequency granularity PMI reporting W1  5 ms/Widebandperiodicity/ frequency granularity PMI reporting W2 5 ms/Widebandperiodicity/ frequency granularity Transmission mode SU-MIMO (Rankadaptation - up to Rank- 2)

TABLE 51 RI reporting periodicity 45 ms CQI reporting periodicity/  5ms/Wideband frequency granularity PMI reporting W1 45 ms/Widebandperiodicity/ frequency granularity PMI reporting W2  5 ms/Subbandperiodicity/ frequency granularity Transmission mode MU-MIMO (Rank-1 perUE, Max 2-Layer pairing) ZF beamforming Codebook subsampling For UE bandselection, all codebook for W1 and subsampling for W2: 2 bit (0, 1, 2,3)

Embodiment 4

W1 and W1 subsampling methods capable of being applied to the case inwhich W1 and W2 are joint-coded will hereinafter be described in detail.

In PUCCH Report Mode 1-1-2 of Table 34, W1 and W2 are transmitted alongwith WB CQI. In Table 34, W1 and W2 are denoted by I1 and I2,respectively. In order to establish a feedback mode that can provide thesame error generation probability as that of the legacy 3GPP LTERelease-8 PUCCH report scheme, the number of bits requisite for theprecoder for each rank may be set to 4.

For example, the number of bits of W1 or W2 according to each rank maybe determined as shown in Table 52. W1 and W2 indexes disclosed in Table52 may respectively correspond to indexes (i1 and i2) of the codebookshown in Tables 11 to 14. Table 52 shows four examples of the W1 and W2subsampling method.

TABLE 52 W1 W2 Rank-1 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} 1 bit: {0, 2}Rank-2 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} 1 bit: {0, 1} Rank-3 1 bit:{0, 2} 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} Rank-4 1 bit: {0, 2} 3 bit:{0, 1, 2, 3, 4, 5, 6, 7} Rank-1 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} 1bit: {0, 2} Rank-2 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} 1 bit: {0, 1}Rank-3 1 bit: {0, 2} 3 bit: {2, 3, 6, 7, 10, 11, 14, 15} Rank-4 1 bit:{0, 2} 3 bit: {0, 1, 2, 3, 4, 5, 6, 7} Rank-1 3 bit: {0, 2, 4, 6, 8, 10,12, 14} 1 bit: {0, 2} Rank-2 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} 1 bit:{0, 1} Rank-3 1 bit: {0, 2} 3 bit: {0, 1, 2, 3, 8, 9, 10, 11} Rank-4 1bit: {0, 2} 3 bit: {0, 1, 2, 3, 4, 5, 6, 7} Rank-1 3 bit: {0, 2, 4, 6,8, 10, 12, 14} 1 bit: {0, 2} Rank-2 3 bit: {0, 2, 4, 6, 8, 10, 12, 14} 1bit: {0, 1} Rank-3 1 bit: {0, 2} 3 bit: {2, 3, 4, 5, 10, 11, 12, 13}Rank-4 1 bit: {0, 2} 3 bit: {0, 1, 2, 3, 4, 5, 6, 7}

Embodiment 5

Embodiment 5 shows the W2 subsampling method capable of being applied toPUCCH Report Mode 2-1.

In PUCCH Report Mode 2-1 of Table 34, if PTI is set to 1 (PTI=1) and SBCQI is transmitted, the SB CQI can be selected in a bandwidth part (BP).That is, WB CQI and WB W2 are reported at a first report time, and theselected SB CQI and the selected band index and SB W2 are reportedwithin a certain BP of the second report time. In Table 38, W1 and W2are denoted by I1 and I2, respectively. At a third report time, SB CQIselected in a BP different from that of the second report time, theselected band index and SB W2 are reported.

In this case, SB CQI is represented by 4 bits or 7 bits. The selectedband index is denoted by 2 bits, and SB W2 is denoted by 4 bits. As aresult, a total sum of bits to be transmitted in one report time (i.e.,one subframe) is set to 10 or 13 bits. However, considering that thenumber of bits of feedback information capable of being transmitted overPUCCH (e.g., in case of using PUCCH Format 2) is limited to 11, a totalnumber of bits must be reduced by 2 bits at Rank-2 or higher.

In order to reduce 2 bits at W2, the W2 subband report of Table 53 maybe used. Table 53 shows two examples in which W2 subsampling is appliedto Rank-2, Rank-3 and Rank-4 under 8Tx antenna transmission.

TABLE 53 W2 Rank-2 2 bit: {0, 2, 4, 6} Rank-3 2 bit: {0, 4, 8, 12}Rank-4 2 bit: {0, 2, 4, 6} Rank-2 2 bit: {0, 2, 4, 6} Rank-3 2 bit: {2,3, 10, 11} Rank-4 2 bit: {0, 2, 4, 6}

In case of the W2 subsampling, the precoder is specified through W1 andW2, such that subsampling may not be applied to W1 so as to prevent theprecoder element from being lost.

As a detailed method for subsampling W2 by 2 bits according toEmbodiment 5, the methods disclosed in various embodiments of thepresent invention can be used.

A method for reporting channel status information (CSI) according to anembodiment of the present invention will hereinafter be described withreference to FIG. 22.

In association with DL transmission from a BS (or eNB) to a UE, the UEmeasures a DL channel state and feeds back the measured result throughuplink. For example, if 8 Tx antennas are applied to DL transmission ofthe BS, the BS can transmit CSI-RS (Channel status information-ReferenceSignal) through 8 antenna ports (Antenna port indexes 15 to 22). The UEmay transmit the DL channel state measurement results (RI, PMI, CQI,etc.) through the CSI-RS. The above-mentioned various examples of thepresent invention can be applied to a detailed method forselecting/calculating RI/PMI/CQI. The BS may determine the number of DLtransmission layers, the precoder, and MCS (Modulation Coding Scheme)level, etc. according to the received channel status information(RI/PMI/CQI), such that it can transmit a DL signal.

In step S2210 of FIG. 22, the UE may transmit an RI at a first subframe.In step S2220, the UE may transmit a first PMI, a second PMI, and awideband (WB) CQI at a second subframe. By a combination of the firstPMI and the second PMI, a UE-preferred precoding matrix can beindicated. For example, the first PMI may indicate candidates of theprecoding matrix applied to the above-mentioned UL transmission, and thesecond PMI may indicate one precoding matrix from among theabove-mentioned candidates.

The subsampled codebook may be applied to the first PMI (i1 or W1) andthe second PMI (i2 or W2). The subsampled codebook may represent acodebook composed of only some indexes of the codebooks shown in Tables11 to 18.

In case of Rank-1 and Rank-2 under the codebook acquired before thesubsampling application, 4 bits are required for the first PMI and 4bits are required for the second PMI. On the other hand, in case ofRank-2 to Rank-4 under the subsampled codebook according to the presentembodiment, the sum of the first PMI and the second PMI is denoted bythe length of 4 bits. In case of Rank-1 or Rank-2, the first PMI mayhave the length of 3 bits and the second PMI may have the length of 1bit. In case of Rank-1, the first PMI may have any one of 0, 2, 4, 6, 8,10, 12, and 14, and the second PMI may have one of 0 and 2. In case ofRank-2, the first PMI may have any one of 0, 2, 4, 6, 8, 10, 12, and 14,and the second PMI may have one of 0 and 1.

In Rank-3 or Rank-4, the first PMI may have the length of 1 bit and thesecond PMI may have the length of 3 bits. In Rank-3, the first PMI mayhave any one of 0 and 2, and the second PMI may have any one of 0, 1, 2,3, 8, 9, 10 and 11. In Rank-4, the first PMI may have any one of 0 and2, and the second PMI may have any one of 0, 1, 2, 3, 4, 5, 6, and 7.

The channel status information (CSI) (i.e., RI, first PMI, second PMI,and CQI) may be transmitted over a PUCCH within each UL subframe. Inother words, CSI may be periodically transmitted, and each CSI (jointcoded RI, first PMI/CQI, and second PMI) may be transmitted in responseto each report cycle. The CSI report cycle may be determined accordingto the above-mentioned various examples of the present invention.

In accordance with the CSI transmission method shown in FIG. 22, eachitem disclosed in various embodiments of the present invention may beindependently applied or two or more embodiments may be simultaneouslyapplied. The same parts may herein be omitted for convenience andclarity of description.

The same principles proposed by the present invention can be applied notonly to CSI feedback for one MIMO transmission between a base station(BS) and a relay node (RN) (i.e., MIMO transmission between backhauluplink and backhaul downlink) but also to CSI feedback for another MIMOtransmission between an RN and a UE (i.e., MIMO transmission between anaccess uplink and an access downlink).

FIG. 23 is a block diagram illustrating an eNB apparatus and a userequipment (UE) apparatus according to an embodiment of the presentinvention.

Referring to FIG. 23, an eNB apparatus 2310 may include a reception (Rx)module 2311, a transmission (Tx) module 2312, a processor 2313, a memory2314, and a plurality of antennas 2315. The plurality of antennas 2315may be contained in the eNB apparatus supporting MIMO transmission andreception. The reception (Rx) module 2311 may receive a variety ofsignals, data and information on uplink starting from the UE. Thetransmission (Tx) module 2312 may transmit a variety of signals, dataand information on downlink for the UE. The processor 2313 may provideoverall control to the eNB apparatus 2310.

The eNB apparatus 2310 according to one embodiment of the presentinvention may be configured to transmit DL transmission through amaximum of 8 Tx antennas as well as to receive CSI of the DLtransmission from the UE apparatus 2320. The processor 2313 of the eNBapparatus 2310 may receive, by the Rx module 2311, a rank indicator (RI)at the first subframe, and may receive a first PMI, a second PMI, and aWB CQI at a second subframe. In this case, a UE preferred precodingmatrix may be indicated by a combination of the first PMI and the secondPMI. In addition, the subsampled codebook is applied to the first PMIand the second PMI, and the sum of the first PMI and the second PMI foreach of Rank-1 to Rank-4 may be composed of 4 bits in the subsampledcodebook.

Besides, the processor 1213 of the eNB apparatus 1210 processesinformation received at the eNB apparatus 1210 and transmissioninformation. The memory 1214 may store the processed information for apredetermined time. The memory 1214 may be replaced with a componentsuch as a buffer (not shown).

Referring to FIG. 23, the UE apparatus 2320 may include a reception (Rx)module 2321, a transmission (Tx) module 2322, a processor 2323, a memory2324, and a plurality of antennas 2325. The plurality of antennas 2325may be contained in the UE apparatus supporting MIMO transmission andreception. The reception (Rx) module 2321 may receive a variety ofsignals, data and information on downlink starting from the eNB. Thetransmission (Tx) module 2322 may transmit a variety of signals, dataand information on uplink for the eNB. The processor 2323 may provideoverall control to the UE apparatus 2320.

The UE apparatus 2320 according to one embodiment of the presentinvention may be configured to receive DL transmission through a maximumof 8 Tx antennas as well as to feed back CSI of the DL transmission tothe eNB apparatus 2310. The processor 2323 of the UE apparatus 2320 maytransmit, by the Tx module 2322, a rank indicator (RI) at the firstsubframe, and may transmit a first PMI, a second PMI, and a WB CQI at asecond subframe. In this case, a UE preferred precoding matrix may beindicated by a combination of the first PMI and the second PMI. Inaddition, the subsampled codebook is applied to the first PMI and thesecond PMI, and the sum of the first PMI and the second PMI for each ofRank-1 to Rank-4 may be composed of 4 bits in the subsampled codebook.

Besides, the processor 2323 of the UE apparatus 2320 processesinformation received at the UE apparatus 2320 and transmissioninformation. The memory 2324 may store the processed information for apredetermined time. The memory 1224 may be replaced with a componentsuch as a buffer (not shown).

In association with the above-mentioned eNB and UE apparatuses, thecontents described in the above-mentioned embodiments may be usedindependently of each other or two or more embodiments may besimultaneously applied, and the same parts may herein be omitted forconvenience and clarity of description.

The eNB apparatus 2310 shown in FIG. 23 may also be applied to a relaynode (RN) acting as a DL transmission entity or UL reception entity, andthe UE apparatus 2320 shown in FIG. 23 may also be applied to a relaynode (RN) acting as a DL reception entity or UL transmission entity.

The above-described embodiments of the present invention can beimplemented by a variety of means, for example, hardware, firmware,software, or a combination of them.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. For example, those skilledin the art may use each construction described in the above embodimentsin combination with each other. Accordingly, the invention should not belimited to the specific embodiments described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above exemplary embodiments are therefore to beconstrued in all aspects as illustrative and not restrictive. The scopeof the invention should be determined by the appended claims and theirlegal equivalents, not by the above description, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. Also, it will be obvious to thoseskilled in the art that claims that are not explicitly cited in theappended claims may be presented in combination as an exemplaryembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

As apparent from the above description, exemplary embodiments of thepresent invention have the following effects. The embodiments of thepresent invention provide a method and apparatus for effectivelyreporting feedback information in a MIMO system. The embodiments of thepresent invention are applicable to a variety of mobile communicationsystems (for example, OFDMA, SC-FDMA, CDMA, and TDMA communicationsystems based on multiple access technology).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of transmitting channel stateinformation (CSI) by a user equipment in a wireless communicationsystem, the method comprising: measuring CSI regarding at least one of arank indication (RI), a precoding matrix indicator (PMI) and a channelquality indicator (CQI); and transmitting the CQI and the PMI via aphysical uplink control channel (PUCCH), wherein in the measurement ofthe CSI, when a value of the RI is lower than a first value and the PMIis indicated by a first PMI value and a second PMI value in a codebookfor 8-transmission antennas, at least one of the first PMI value and thesecond PMI value is obtained from a sub-sampled codebook of thecodebook.
 2. The method of claim 1, wherein the first value is 5 and thecodebook corresponds to one of a Rank 1-codebook, a Rank 2-codebook, aRank 3-codebook and a Rank 4-codebook.
 3. The method of claim 1, whereinwhen the value of the RI is equals to or greater than the first valueand the PMI is indicated by the first PMI value and the second PMIvalue, the first PMI value and the second value are obtained from thecodebook instead of the sub-sampled codebook.
 4. The method of claim 1,wherein when the value of the RI is equals to a second value smallerthan the first value, and the PMI is indicated by the first PMI valueand the second PMI value, the first PMI value is obtained from thesub-sampled codebook and the second PMI value is obtained from thecodebook.
 5. The method of claim 1, further comprising: receiving atleast one of a cell-specific reference signal and a CSI-reference signalfrom a base station; and transmitting the RI via the PUCCH on a firstsubframe, wherein the CSI is measured based on at least one of thecell-specific reference signal and the CSI-reference signal, and whereinthe PMI and the CQI are transmitted on a second subframe other than thefirst subframe.
 6. The method of claim 1, wherein a subsampling rate forthe sub-sampled codebook depends on the value of the RI.
 7. The methodof claim 1, wherein when the value of the RI is 1 or 2, half of firstPMI value candidates in the codebook are available in the sub-sampledcodebook, and ⅛ of second PMI value candidates in the codebook areavailable in the sub-sampled codebook.
 8. The method of claim 1, whereinif the value of the RI is 3, ½ of first PMI value candidates in thecodebook are available in the sub-sampled codebook, and half of secondPMI value candidates in the codebook are available in the sub-sampledcodebook.
 9. The method of claim 1, wherein if the value of the RI is 4,½ of first PMI value candidates in the codebook are available in thesub-sampled codebook, and all of second PMI value candidates in thecodebook are available in the sub-sampled codebook.
 10. The method ofclaim 1, wherein when the value of the RI is lower than the first valueand the PMI is indicated by the first PMI value and the second PMIvalue, a sum of a size of the first PMI value and a size of the secondPMI value is 4-bit.
 11. The method of claim 1, wherein when the value ofthe RI is equals to or greater than the first value and the PMI isindicated by the first PMI value and the second PMI value, a sum of asize of the first PMI value and a size of the second PMI value is 2 or0.
 12. The method of claim 1, wherein when the value of the RI is 1 or 2and the PMI is indicated by the first PMI value and the second PMIvalue, a size of the first PMI value is 3-bit and a size of the secondPMI value is 1-bit.
 13. The method of claim 1, wherein when the value ofthe RI is 3 or 4 and the PMI is indicated by the first PMI value and thesecond PMI value, a size of the first PMI value is 1-bit and a size ofthe second PMI value is 3-bit.
 14. The method of claim 1, wherein whenthe value of the RI is 1, the codebook is represented by the followingtable: i₂ i₁ 0 1 2 3 4 5 6 7 0-15 W_(2i) ₁ _(,0) ⁽¹⁾ W_(2i) ₁ _(,1) ⁽¹⁾W_(2i) ₁ _(,2) ⁽¹⁾ W_(2i) ₁ _(,3) ⁽¹⁾ W_(2i) ₁ _(+1,0) ⁽¹⁾ W_(2i) ₁_(+1,1) ⁽¹⁾ W_(2i) ₁ _(+1,2) ⁽¹⁾ W_(2i) ₁ _(+1,3) ⁽¹⁾ i₂ i₁ 8 9 10 11 1213 14 15 0-15 W_(2i) ₁ _(+2,0) ⁽¹⁾ W_(2i) ₁ _(+2,1) ⁽¹⁾ W_(2i) ₁ _(+2,2)⁽¹⁾ W_(2i) ₁ _(+2,3) ⁽¹⁾ W_(2i) ₁ _(+3,0) ⁽¹⁾ W_(2i) ₁ _(+3,1) ⁽¹⁾W_(2i) ₁ _(+3,2) ⁽¹⁾ W_(2i) ₁ _(+3,3) ⁽¹⁾${{where}\mspace{14mu} W_{m,n}^{(1)}} = {\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m} \\{\phi_{n}v_{m}}\end{bmatrix}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), values 0 to 15 of i₁correspond to 16 first PMI value candidates in the codebook, and values0 to 15 of i₂ correspond to 16 second PMI value candidates in thecodebook, and wherein only 0, 2, 4, 6, 8, 10, 12 and 14 of i, from amongthe 16 first PMI value candidates and only 0 and 2 of i₂ from among the16 second PMI value candidates are available in the sub-sampledcodebook.
 15. The method of claim 1, wherein when the value of the RI is2, the codebook is represented by the following table: i₂ i₁ 0 1 2 30-15 W_(2i) ₁ _(,2i) ₁ _(,0) ⁽²⁾ W_(2i) ₁ _(,2i) ₁ _(,1) ⁽²⁾ W_(2i) ₁_(+1,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,1) ⁽²⁾ i₂ i₁ 4 5 6 70-15 W_(2i) ₁ _(+2,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+2,2i) ₁ _(+2,1) ⁽²⁾W_(2i) ₁ _(+3,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁ _(+3,1) ⁽²⁾ i₂ i₁ 89 10 11 0-15 W_(2i) ₁ _(,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁ _(,2i) ₁ _(+1,1) ⁽²⁾W_(2i) ₁ _(+1,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+2,1) ⁽²⁾ i₂ i₁ 1213 14 15 0-15 W_(2i) ₁ _(,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(,2i) ₁ _(+3,1)⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+3,1) ⁽²⁾${{where}\mspace{14mu} W_{m,m^{\prime},n}^{(2)}} = {\frac{1}{4}\begin{bmatrix}v_{m} & v_{m^{\prime}} \\{\phi_{n}v_{m}} & {{- \phi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), values 0 to 15 of i₁correspond to 16 first PMI value candidates in the codebook, and values0 to 15 of i₂ correspond to 16 second PMI value candidates in thecodebook, and wherein only 0, 2, 4, 6, 8, 10, 12 and 14 of i, from amongthe 16 first PMI value candidates and only 0 and 1 of i₂ from among the16 second PMI value candidates are available in the sub-sampledcodebook.
 16. The method of claim 1, wherein when the value of the RI is3, the codebook is represented by the following table: i₂ i₁ 0 1 2 3 0-3W_(8i) ₁ _(,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ W_(8i) ₁ _(+8,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾{tilde over (W)}_(8i) ₁ _(,8i) ₁ _(+8,8i) ₁ ₊₈ ⁽³⁾ {tilde over (W)}_(8i)₁ _(+8,8i) ₁ _(,8i) ₁ ⁽³⁾ i₂ i₁ 4 5 6 7 0-3 W_(8i) ₁ _(+2,8i) ₁ _(+2,4i)₁ ₊₁₀ ⁽³⁾ W_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁ ₊₁₀ ⁽³⁾ {tilde over (W)}_(8i)₁ _(+2,8i) ₁ _(+10,8i) ₁ ₊₁₀ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+10,8i) ₁_(+2,8i) ₁ ₊₂ ⁽³⁾ i₂ i₁ 8 9 10 11 0-3 W_(8i) ₁ _(+4,8i) ₁ _(+4,8i) ₁ ₊₁₂⁽³⁾ W_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁ ₊₁₂ ⁽³⁾ {tilde over (W)}_(8i) ₁_(+4,8i) ₁ _(+12,8i) ₁ ₊₁₂ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+12,8i) ₁_(+4,8i) ₁ ₊₄ ⁽³⁾ i₂ i₁ 12 13 14 15 0-3 W_(8i) ₁ _(+6,8i) ₁ _(+6,8i) ₁₊₁₄ ⁽³⁾ W_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁ ₊₁₄ ⁽³⁾ {tilde over (W)}_(8i) ₁_(+6,8i) ₁ _(+14,8i) ₁ ₊₁₄ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+14,8i) ₁_(+6,8i) ₁ ₊₆ ⁽³⁾${{{where}\mspace{14mu} W_{m,m^{\prime},m^{''}}^{(3)}} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & {- v_{m^{\prime}}} & {- v_{m^{''}}}\end{bmatrix}}},{{\overset{\sim}{W}}_{m,m^{\prime},m^{''}}^{(3)} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & v_{m^{\prime}} & {- v_{m^{''}}}\end{bmatrix}}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), values 0 to 3 of i₁correspond to 4 first PMI value candidates in the codebook, and values 0to 15 of i₂ correspond to 16 second PMI value candidates in thecodebook, and wherein only 0 and 2 of i, from among the 4 first PMIvalue candidates and only 0, 1, 2, 3, 8, 9, 10 and 11 of i₂ from amongthe 16 second PMI value candidates are available in the sub-sampledcodebook.
 17. The method of claim 1, wherein when the value of the RI is4, the codebook is represented by the following table: i₂ i₁ 0 1 2 3 0-3W_(8i) ₁ _(,8i) ₁ _(+8,0) ⁽⁴⁾ W_(8i) ₁ _(,8i) ₁ _(+8,1) ⁽⁴⁾ W_(8i) ₁_(+2,8i) ₁ _(+10,0) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁ _(+10,1) ⁽⁴⁾ i₂ i₁ 4 5 6 70-3 W_(8i) ₁ _(+4,8i) ₁ _(+12,0) ⁽⁴⁾ W_(8i) ₁ _(+4,8i) ₁ _(+12,1) ⁽⁴⁾W_(8i) ₁ _(+6,8i) ₁ _(+14,0) ⁽⁴⁾ W_(8i) ₁ _(+6,8i) ₁ _(+14,1) ⁽⁴⁾${{where}\mspace{14mu} W_{m,m^{\prime},n}^{(4)}} = {\frac{1}{\sqrt{32}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m} & v_{m^{\prime}} \\{\phi_{n}v_{m}} & {\phi_{n}v_{m^{\prime}}} & {{- \phi_{n}}v_{m}} & {{- \phi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

where φ_(n) is denoted by φ_(n)=e^(jπn/2) and v_(m) is denoted byv_(m)=[1 e^(j2πm/32) e^(j4πm/32) e^(j6πm/32)]^(T), values 0 to 3 of i₁correspond to 4 first PMI value candidates in the codebook, and values 0to 7 of i₂ correspond to 8 second PMI value candidates in the codebook,and wherein only 0 and 2 of i, from among the 4 first PMI valuecandidates and all of the 8 second PMI value candidates are available inthe sub-sampled codebook.
 18. A user equipment for transmitting channelstate information (CSI) in a wireless communication system, the userequipment comprising: a processor configured to measure CSI regarding atleast one of a rank indication (RI), a precoding matrix indicator (PMI)and a channel quality indicator (CQI); and a transmitter configured totransmit the CQI and the PMI via a physical uplink control channel(PUCCH), wherein when a value of the RI is lower than a first value andthe PMI is indicated by a first PMI value and a second PMI value in acodebook for 8-transmission antennas, at least one of the first PMIvalue and the second PMI value are obtained from a sub-sampled codebookof the codebook.
 19. A method of receiving channel state information(CSI) by a base station in a wireless communication system, the methodcomprising: receiving CSI via a physical uplink control channel (PUCCH);and obtaining a precoding matrix indicator (PMI) and a channel qualityindicator (CQI) from the CSI, wherein in the obtaining the PMI, when arank indicator (RI) value is lower than a first value and the PMI isindicated by a first PMI value and a second PMI value in a codebook for8-transmission antennas, at least one of the first PMI value and thesecond value belongs to a sub-sampled codebook of the codebook.
 20. Abase station for receiving channel state information (CSI) in a wirelesscommunication system, the base station comprising: a receiver configuredto receive CSI via a physical uplink control channel (PUCCH); and aprocessor configured to obtain a precoding matrix indicator (PMI) and achannel quality indicator (CQI) from the CSI, wherein when a rankindicator (RI) value is lower than a first value and the PMI isindicated by a first PMI value and a second PMI value in a codebook for8-transmission antennas, at least one of the first PMI value and thesecond value belongs to a sub-sampled codebook of the codebook.